Back-Focus 101: DSLR Cameras & the Celestron f/6.3 Reducer/Corrector

[@AstroBlender]

A big thanks to @TwoHandUke for pointing out the error in the first version of this video, which has since been corrected.

[@ash20500]

What should the backfocus distance be without the focal reducer?

[@blaircolliver5194]

Thanks very much! I had questions about the use of the focal reducer and your video explained everything perfectly.

[@trader025]

Good lord such a clear and complete explanation of BF length. Nice!

[@MCDanyification]

Nice video! Do you know the normal bckfockus of the Celestron without the reducer. Just for planetary imaging?

[@HollomanUFOLanding]

Hi Cody, thanks for another informative and interesting video. They are all appreciated. Would you consider making a presentation on eyepiece projection imaging? I would love that and I am sure many others would, too!!! Thanks!!!

[@tommy8644]

HI, is it possible to put a 2" filter with this configuration? thanks

[@edwardgill1042]

Most may not know it but the Back-focus standard for T adapters is 55mm regardless of camera type. If you have a mirrorless camera that has a registry (back-focus) distance of 20mm, the T adapter will be 35mm deep. There are "Short" T adapters that do not follow the 55mm standard but if you're buying on of those you're probably already aware of how to get to the proper back focus. Note, many refractor reducer/correctors are designed with a 55mm back-focus so that they just screw into standard T adapters without additional spacer rings/tubes.

[@northernpcp]

I just love your videos. I am a newbie and you explain so many things with such clarity. I'm about to purchase a canon Eos 60d and being a newbie, didn't even know of the Celestron SC adaptor. I have a C8. Many many thanks. stay safe..stay happy. ....regards...Dave

[@miltonkgeedvm]

Thank you Simon.

[@thomasrider5852]

This was insanely helpful thank you!

[@wicklowjohn]

thanks for the video. extremely informative and to the point.

[@i8d0m8a2]

I appreciate this video helped me out a lot!

[@jeffslade1892]

Whilst the Canon EF system is 44.0mm, the flange focal distance varies wildly with other makes (Pentax K is 45.46mm). There will be a focal plane mark on the camera, a circle with a line through it. In astronomy we call it back-focus but in general photography that is a very different term, a button on the camera - it's 'flange focal distance'. With mirrorless systems it is much shorter, micro-four-thirds is 19.25mm. This makes rigging a camera onto an OTA a lot of fun.

[@AstroBlender]

Correct! The short distance on the mirror less is actually nice though. Much more room for accessories.

[@josecolonii7742]

What if I want to add a filter between the DSLR and the focal reducer? I have a filter to reduce city lights a bit and want to try that. How do I get to that 105mm distance and get the filter inline.

[@dneurona]

Thanks for the video! Will this work on a celestron astrofi 102mm?

[@oldmombasa7]

If I understand that correctly, I have to add the Mount Adapter EF-EOS R with 25 mm to a Canon EOS-R, which only has a flange focal length of 20 mm. So that I can reach 45 mm.

[@alain.s730]

Hello, with the installation shown in your video, can we install a 2" filter for astrophoto. I have a Celestron C-8 with a focal reducer f 6.3 if yes and how without disturbing the backfocus. Thank you Alan

[@ironian24]

brilliant thank you, I have a Canon m6 mkii mirrorless cropped sensored camera, what would I need for that?

[@jeffslade1892]

You need to know the flange focal distance and set the lens at the right distance from the sensor. You will need different length spacer tubes

[@josevega7581]

Nice Video, can you please make a similar video on how to Back focus with a Barlow.

[@doco6186]

Cool. Lots of information per unit time.

[@koolkutz7]

Nice explanation. Got all the rquired gear, just going to wait a while now until the nights start drawing in before I do some imaging :-)

[@AstroBlender]

Steve Ferneyhough Cool, enjoy!

[@hobbeeswe7472]

Great video! I am looking to get either Celestron C6 or C8 scope with a Celestron AVX and use it with my Canon EOS 70D (APS-C sensor), autoguiding with the help of a ZWO ASIAIR Mini. I am wondering about how to insert a filter/filter drawer/filter wheel. I looked at the ZWO EFWmini 1,25" and a simple ZWO filter drawer. What would you suggest and can the standard image train work with 1,25" filters? Many thanks in advance.

[@666milek666]

In this adapter->visual back system, it is not possible to install a 1.25" filter. Only the filter inside the camera?

[@javiricci1010]

Muy buen video. Y para conectar un OAG + dslr + reductor? Es posible?

[@gjman1972]

Hi I love your videos and I just ordered my Celestron nexstar 8se with the goal of astrophotography and I have a question I’m hoping you can answer. My question is do the sky portal WiFi adapter, the sky sync gps, and star sense all do the same thing? I have ordered all 3 and I’m wondering if I can I use or need all 3 or is there a best one or combination of the 3 items I described for aligning and making the telescope as easy to use for astrophotography? Thank you!

[@omarlorentz99]

Hi video very good, thanks.If i have to put an off axis guide i have to find a combination of extensions by eliminating the celestronn adapter?

[@gomcse]

Brilliant. Thank you!

[@Holographic_Meatloaf252]

I have this exact setup with a canon 1000d but am still disappointed with the star flanging around the edges.

[@mediabyjw]

if i want to add a filter. where is that going in? :)

[@kimex5164]

how is it with a star diagonal? Im scared that it would be to long and touch the mount when its aligning and slewing. I got the cne 9,25 but cant get it the right focus when i use 2"

[@michaelfrazier9537]

So, I am new to this. My son-in-law gave his Canon EOS Rebel 3t. What should my shutter speed be set to and any other setting you can recommend? Thank you!

[@cj-nj7vt]

Just bought a dslr canon 600d now I know what connections to use with my celestron 8"sct without figuring out the maths thanks.

[@Jdiracer17]

I’ve been searching wide for answers with no straight answer, do you have a solution to fit a filter drawer or wheel into this solution?

[@AlmightyAddman]

Helpful video thanks

[@deborahburd5876]

does this process also work on Olympus mirrorless...thank you

[@kc9161]

Has anyone tried combining two of this 0.63 reducer to form f3.9? Wonder what the back focus would be.

[@slzckboy]

On most "canon EF lens " Dslrs. Backfocus varies for different manufacturers/mount tyoes

[@Meow-Mix1041]

Ha! I have that same shirt!! Super informative video! Thanks!! Love your chanel

[@AstroBlender]

Awesome! Glad you liked it.

[@kennethschroeder2789]

Would this Celestron focal reducer work with a Meade LX90 ACF 8" scope? I have 1-1/4" eyepieces. Thanks for any advice. Ken

[@jdogbirdeye]

Thanks for sharing ,I have a question,, I have tried to use Lumix G9 which is micro 4 3rd, but having problems with viewing the whole subject in & it seems to crop the image which makes it impossible to take a full image of the moon

[@upnorthoffcuts929]

I am assuming that this would not be the case for deep sky imaging and not needing the reducer. If not what would be the back focus for a DSLR for an 8se?. Thanks for the content, this was helpful. John.

[@AstroBlender]

If you have a “standard SCT” it’s around 5in. www.celestron.com/blogs/knowledgebase/what-are-the-optimum-back-focus-distances-for-celestron-scts

[@AstroBlender]

An EdgeHD SCT has a built in field flattener, so back focus is set by the flattener and must be adhered to for best results.

[@AGM-Prism]

I'm running this same setup (Nikon, but similar flange/sensor distance) but I still have an unflat field and bad coma towards the edges, any ideas? I'm a beginner so any tips would be much appreciated!

[@leboch65]

What about if i decided to use the celestron 1.25 diagonal , t adaptor and my dslr? What is the distance of the celestron diagonal?

[@1701c14]

Thanks for this video. How much vignetting would I get with this configuration using a Full Frame Canon 6D on a Cellestron C11?

[@RaggsM]

Hi did you find the answer to your question? I need to do the same

[@brettatton]

I looked up Canon and it is 44mm for the EF-S and EF bodies.

[@MrBrianontyne]

Howdy am using a celestron 130 astromaster and a canon 250 dslr can you advise what all need to do astro photography with it cheers.

[@erentunali7228]

Can I use a Barlowlense with the T-Adapter ?

[@hugopritchard8455]

In addition to a couple of DSLR cameras, I own a SBIG 8300 C. I use a 2 inch Visual Back to attach it. What is the back focus if I use a reduce corrector, the f/6.3 for example? My OTA is a C8.

[@alexkim3295]

Am I allowed to use any type of t-adapter or does it have to be specifically for Schmidt cassegrain?

[@videoman77365]

would I need this on the Celestron NexStar Telescope- 6in to take photos? I have a d7200 Nikon

[@Franco-Zana]

How do you know how much backfocus do you need for any telescope?

[@matchewbacca]

Right a couple of questions from a newbie is this distance the same for apsc cameras ? Also is there a set distance too without the focal reducer or the same 105 mm from sensor Thanks

[@gautieralt4496]

Good afternoon @AstroBlender, Thanks a lot for the vidéo. I have a Celestron Nexstar 4 SE and I would like to buy the Focal Reducer. I have a problem because I don't think that the reducer fits at the back of my scope. Have you already tried with a 4SE? Thanks in advance!

[@YM-qb6gh]

I’m having the same problem, but with an slt 127mm telescope. Did you find a focal reducer that worked?

[@nathanriebe1484]

hey is there any chance you could post the link to the t ring you used

[@gatogidh1898]

I bought the "T-Adapter for 8” EdgeHD optical tube threads onto the rear cell" previously, but I'm thinking about buying the focal reducer. Will it work with that t adapter that I already have or do I have to buy the focal reducer and the t adapter package?

[@AstroBlender]

If you have the Celestron 8” EdgeHD T-Adapter it will work with the 0.7X reducer, but you must remove the top piece of the T-adapter and shorten it.

[@gatogidh1898]

@AstroBlender Okay, thank you so much, I can now but it with no doubts and with peace in mind 😌

[@yervantparnagian5999]

What should I do if I'm connecting a NIkon Z mirrorless camera?

[@onurboga1507]

I have a ZWO ASI462 dedicated astronomy camera. Does this 105 mm also apply to this kind of cameras? I think, the sensor to flange distance is in this case lower. How long should be the back focus in this case?

[@wanderingquestions7501]

The most easy way to show a user what back focus is would be on a refractor. Let’s say yours is 420mm FL. Find where the lens is in the front of the refractor. Then take a tape measure and measure 42 cm back from the front lens. Did you see that length passes the end of your rack focuser. That’s where your focal plane is at. Putting spacers and camera together is done so your gear can focuses at the focal plane.

[@davideb.7533]

I have question i have focal reducer to and i got problem with canon r6 i have big viegnet problem 😔

[@qonos68]

You have to take flats.

[@amaimani]

Can u help me with the proper distancing for ASI294 used on SCT8 with focal length of 1600mm please?

[@Aguilestri]

Hy there thanks!! One question. Where you found the information about Back-Focus required? I have a Meade reducer f/3.3, how calculate this? Thank you.

[@kisho2679]

Is it suitable to redece a focal length of 2800mm (SC11 tubus) for Deepsky-Photography with Off-Axis-Guiding (OAG)?

[@Vivekananda-l3h]

Thanku sir

[@mikedesverknopf4681]

I have a Panasonic G7. Any differences?

[@AstroBlender]

Yes, I think the back focus from sensor to flange on a G7 is 19.25mm, so you would need additional adapters to get the spacing right.

[@pulver117]

any way to add a 2" filter using these adapters? or what would be a work around without using clip in filters?

[@AstroBlender]

pulver117 The easiest thing to do is use a filter drawer. ZWO, Starizona, etc. these will take up some backspace and may allow you to remove one of the adapters in the chain depending on how thick the filter drawer is.

[@pulver117]

@@AstroBlender would i need a filter drawer to be between the focal reducer/corrector and scope to prevent changing backspace from that 105mm? What thread size is the back of the nexstar's?

[@AstroBlender]

pulver117 Sorry I didn’t realize this was for the DSLR version of the video, I thought it was CCD. You could try the filter drawer with no SCT t-adapter, and then add spacers with the final one being an SCT female thread.

[@pulver117]

@@AstroBlender No worries, and yeah i thought about try to figure out spacers and all but i just ended up purchasing the Astronomik full frame clip in filters to make life easier, still learning. thanks for the help, and thanks for the helpful vids.

[@AstroBlender]

pulver117 Yep, that’s what I did too a long time ago! Enjoy!

[@gianlucalombardi1026]

can you tread 1.25" filters into the T Adapter? is there a solution for that?

[@edwardgill1042]

Gianluca. Most T adapters for astronomy have a nose piece that slides into the focuser. If the nose piece is 1.25 inch they USUALLY accept 1.25 inch filters screwed into the telescope end of the nose piece. If they have a 2 inch nose piece for a 2 inch focuser, they USUALLY accept 2 inch filter. I say USALLY because you need to check before you buy if the nose piece is threaded for filters. The Celestron SC T adapter shown in the video does not have a place for filters to my knowledge, but there are other solutions.

[@gianlucalombardi1026]

@@edwardgill1042 thanks a lot

[@troubydoo]

Hi Slymin. Great great video. You hit on some very common equipment and use cases. I am just a tiny bit confused on backfocus as I build out my own similar setup. I have a Celestron Electric focus motor, a celestron focal reducer, various cameras , and an astromania 9 spot filter wheel. My cameras are: ZWO 120mc-s ZWO 294mm mini Svbony 205 Neximage 10 by Celestron My scope is the standard Celestron 8” SCT. I also just got the ZWO OAG. I do have the canon T adapter for my DSLR and watched the videos about using that to get 50mm more space. So with a focal reducer and without a focal reducer and could I just focus with my electric focus motor? Is the backfocus that important? I am learning here but took the plunge. I haven’t put in the OAG yet but plan too. I do want a good setup with and without that reducer. Please help clarify. Thank you much! Robbie

[@troubydoo]

Also some videos say 105mm of back focus while others say 55mm of backfocus. I think that is with or without the focal reducer from what I understand.

[@deborahburd5876]

Question when I put on the focal reducer on my Celestron and I do a live view and also take a photo I get a circular vignette around the subject. How do I correct this?

[@AstroBlender]

You need to take flat frames.

[@juanpipila1]

Hi, can you give us a link in Amazon for purchase T adapter (i have a Nikon T-ring to put in the star diagonal) my focal reducer arrived yesterday. Greetings from Chile.

[@juanpipila1]

Finally i found in Amazon.

[@gianniformica8235]

If your not using the reducer what is the backfoscuse?

[@AstroBlender]

Wherever your camera focuses. No set requirement.

[@ivanaguilar2827]

I would like to attach my DSLR to my SC8 like that but use 2" filters,how do I do that? right now I use a diagonal 2"

[@jerrysamuelson1247]

Your T-Ring for your particular brand of camera will thread onto the T thread adapter. I do believe that I am having some focusing issues though and I'm hoping that these items haven't increased my back focus too much. I believe that it's more operator error, I hope.

[@thefourgrapples2810]

So with the reducer the back focus is 105mm, what is the back focus without the reducer?

[@AstroBlender]

It depends on the SCT. For a C8 it’s 5 inches from the primary mirror baffle tube lock ring. I usually just use the T-Ring and SCT adapter and when I get focus call it good.

[@thefourgrapples2810]

@@AstroBlender Thank you.

[@AstroBlender]

TheFourGrapples No problem.

[@okeania]

You should have warn people forehand if you use this method they can't add additional filter. Only Clip filter can add to camera.

[@jbflores01]

I have a meade lx200 8" SCT with a meade 6.3 focal reducer. I use the 2"sct adapter to attach my DSLR to the back of the reducer to give me the "correct" back focus. My problem is that even with the focal reducer with "correct" back focus still gives me coma. the coma "point" away from the center. I believe this is a diagnostic of incorrect back focus. Which way do I go, add or remove more back focus. any suggestions are appreciated.

[@patterdalezipsuzilil]

Dslr are to heavy and the shutter shakes the scope