HFR, HFD, FWHM... What ARE THEY??

We see HFR, HFD, FWHM acronyms thrown around in astrophotopgraphy a lot, but what exactly are they? What are they used for? Why use one over another? How are they computed?
Let's go into the details!
Link to the spreadsheet I use in this video: docs.google.co...
My Instagram: / cuivlazygeek
My Facebook page: / cuivlazygeek
#astrophotography

[@ChucksAstrophotography]

HFR, HFD, FWHM...I've heard of them all and never used any of them, lol. CORRECTION: I use HFR all the time, oops.

[@CuivTheLazyGeek]

Hahaha, yes Chuck, we do see you use HFR all the time! :D Thanks for dropping by!

[@FrootyRecords]

Do you know all this time I was trying to get my FWHM in Sharpcap as low as your.. (what I now know is ) HFR, thinking 'How does Chuck the magician do it' :) hehe.

[@qlifee]

I really appreciate your laziness, it is the reason I watch your videos 🦥

[@CuivTheLazyGeek]

Laziness is my way of life :) Thanks for watching!

[@davidaylsworth8964]

There’s nothing lazy about this video. Name change to “Cuiv, the over-achieving geek” is in order. Well done video Sir! It really helps me understand focus issues and the particulars used to calculate the metrics.

[@cizirf143]

Great video Cuiv, simple words for a quite complex concept... congrats !!!

[@CuivTheLazyGeek]

Thank you!!!

[@FrootyRecords]

I really learnt a great deal from this one Cuiv. The time it must take you to do all that spreadsheet stuff, let alone make the actual video! Thanks again for your efforts in producing these quality videos for us.

[@CuivTheLazyGeek]

Good to hear it was instructive! I typically don't spend a huge amount of time on videos, but yes, this one was an exception - but a lot of fun at the same time. And I learned a lot as well! Thanks again and Clear Skies!

[@srn4couk]

Cuiv, really to echo what others have said. I have been gradually advancing with astrophotography for about a year now. I don't have anyone local to me who is experienced with it, and like everybody says, there is a big hill to climb in learning and applying knowledge. It has been web sites and KZbin channels that have been key to my making progress. I like the pace and level of detail of your tutorials, they are insightful and well presented. I look forward to your future videos with anticipation. Thanks for your efforts ! Nick

[@CuivTheLazyGeek]

I am so happy to see that my efforts, as well as other KZbinr's efforts can have such a positive impact! Thanks for the feedback Nick!

[@alpsalish]

Cuiv, you may not have the interest or the time, but I would love and find very valuable a separate video diving into the the pixel brightness/index plotting workflow and flux analysis. Honestly, I get the concepts, but feel there is more to be gleaned for me from seeing the process. I don't know if there is interest from the community or if you have already created this video, but would love to hear back. You're doing great things I wish you many more subs.

[@cheloniachris]

Great video, again! Where many other astro-youtubers around have the 60th review of e.g. the Pegasus Power Box, many of your videos have quite unique and valuable content. Thanks for your contributions!

[@CuivTheLazyGeek]

Hahaha, I do try to have very unique (and probably too technical) content. Thanks for the feedback!

[@whatmattersmost6725]

It's a blast and you are a BLAST! Just great Cuiv!

[@CuivTheLazyGeek]

Thank you Christopher!

[@Alex_Mastino]

I'm discovering your channel, I'm learning a lot of things, subscribed ! Realy thank you for your job, approach and objectivity on the tests ! Ps: congratulations for results with your location... !

[@peitaoyan1000]

It's been great watching your videos and understanding from the very basics to the technical backgrounds of astrophotography!

[@CuivTheLazyGeek]

Excellent, to hear, thanks for the feedback!

[@swagonman]

Thanks for the video. My question is: can you please explain the spot diagrams that some telescope makers are publishing on the website for their scopes? How do these affect resolution? How do they interplay with the pixel size of a sensor? Why is the manufacturer showing us this information; what are they trying to convey? I ask because in terrestrial lens reviews, sharpness is always a major part of the review. However, in astrograph telescope reviews, it almost seams like sharpness isn’t a major concern. Flatness of focal plane and star roundness shape are instead the major concerns. Sharpness (resolving power) is “calculated” with respect to the aperture size, primarily. But when I compare spot diagrams, I see huge differences between scopes with similar aperture and focal length. Does it matter? Intuitively, I think it does. For example, compare a RedCat 71 vs. GT81 with 0.8x vs. Zenithstar 73 and 81 with 0.8x vs. Fluorostar 91 with 0.8x. Add to that the spot diagrams from similar offerings of Askar, ZWO, etc. It seems like the RedCat wins against the bigger scopes. Only the very center of the frame from the big Fluorostar 91 is sharper. Am I understanding this correctly? And all of these spot diagrams seem to be larger than the airy disk calculation. (What does diffraction limited mean, anyway, with respect to imaging?) The spot diagrams are also much larger than the 3.76um pixel size of the 2600 and 6200 series cameras. (So much for being under-sampled?) I think if I don’t crop in, it might not make so much difference. But if I print large (13x19” for example) or crop in, then it must make a big difference. I probably won’t buy a longer focal length scope for smaller targets, at least for several years. So resolution and cropping matter to me for purchasing my first wide-field astrograph refractor. Anyway, any insight you have is appreciated. If you make a video on comparing spot diagrams and how/if it matters, that would be great!! From my terrestrial photography perspective experience, lens sharpness does matter. I don’t believe it is wise to use an online calculator to check if your pixel image scale is good or not when that calculator ignores the actual optics. From these spot diagrams, clearly the optics are less than perfect enough to matter, if I’m understanding this correctly.

[@johnjames378]

Once again another super video. Have you decided to image Neowise with your DSLR?

[@CuivTheLazyGeek]

Well I want to image Neowise, but the rainy season in Japan doesn't agree....

[@juanmanuelgil3103]

Great video! Would you mind enabling the automatic translations for this video? All the others videos from you that I have checked do have translations, and it's super hard for me to follow English otherwise. Thank you!

[@robertcalise8634]

Thanks for clarifying all that.Very interesting stuff

[@CuivTheLazyGeek]

My pleasure, thanks for watching :)

[@michaellewis7768]

Thanks for this video! I've been in this hobby for 6 months now, so I know I should have understood what these terms meant before this.It's just that the learning curve for this hobby is so steep, I think my brain kind of gave out on this nugget of information. lol! I currently use the ASIAIR Pro which uses HFD for focusing, but I just resorted to using a Bahtinov mask to avoid learning a new thing. I may give it a try again, maybe. :-)

[@CuivTheLazyGeek]

My pleasure Michael, I'm glad it is being useful! Technical videos typically perform much less well than non-technical one (this one seems to be no exception), but I know they can be very useful to understand what all those terms are. For the HFD in the AsiAir Pro, it basically is just that you want to find the lowest HFD possible. However, the AsiAir doesn't have an Autofocus routine, so it may be better for now to keep using the Bahtinov mask, as it should be more precise than trying to manually find lowest HFD (vs an autofocus method that would accurately find that point),

[@phcalama]

@@CuivTheLazyGeek As I'm sure you know, but perhaps others don't, the ASIAir app now has an Autofocus routine

[@mathiasboehme]

Thank you for not doing another video of Neowise... hopefully you got already a clear night to observe this nice comet anyway ;-)

[@CuivTheLazyGeek]

Unfortunately no! There has not been a single nighttime break in the clouds yet! I really, really want to be able to see it. If it were not for COVID-19, I probably would have flown out from Japan to reach a region with better weather...

[@mathiasboehme]

Cuiv, The Lazy Geek That’s bad news... wish you clear skies from now on! BTW, speaking of HFR/ HFD, this reminds me of PFJ and JPF, know what I mean :-D

[@OrionM42]

Technical things simplified....👍🏽

[@CuivTheLazyGeek]

Maybe that should be the name of my channel :)

Audio goes out of sync Cuiv: Nah, too lazy. Brilliant explanation and especially plotting real data btw! Too much information and represented very well.

[@CuivTheLazyGeek]

Hahaha, sorry about that!! Glad you found this well presented and useful!

[@robertojimenez5788]

Thanks for the video Cuiv, how do you export the data from pixinsight to the spreadsheet?

[@CuivTheLazyGeek]

I used this tool here: www.think-maths.co.uk/spreadsheet . It "added" color data to my image, which I manually removed, but otherwise it worked great!

[@robertojimenez5788]

@@CuivTheLazyGeek Oh my God !! Hahaha. You're the best. I'll try it. I see that only works with data between 0 and 255 values but despite this it is very interesting. Your videos are superb. Thank you very much!!

[@OlliesSpace]

Well explained Cuiv

[@salomon1639]

great explanation-thanks

[@CuivTheLazyGeek]

Glad it was helpful!

[@redabdab]

I understand what HFR, HFD, FWHM are. But I don't understand why the mean weighted distance divided by the mean pixel value gives you the HFD. What's the mathematical reason for this?

[@tostativerdk]

Very useful!

[@anata5127]

Seeing is measured in FWHM. If I have HFR from NINA, how could I calculate FWHM?

[@jonathanm3488]

Can you take the image resolution as determined by dividing (HFD arcsecs/HFD pixels), and compare that to the limit of your imaging resolution based on camera/OTA combination? Then using those values to determine atmospheric seeing? For example if HFD resolution is 2.8, but my OTA/Camera resolution is .5, then the atmospheric seeing is 2.3?

[@arnaudmarie2892]

I understand the reasoning of this video in the case of a monochrome sensor. But how can we apply this reasoning to a Bayer matrix color sensor. Indeed, the apparent resolution of the Bayer matrix is lower than that of a monochrome matrix.

[@CuivTheLazyGeek]

Yeah, with the Bayer matrix we Debayer first, and then convert back to monochrome. So you will naturally get a somewhat higher HFR, but not by much.

[@space.explore]

Hi, how can I find out FWHM of my subframes without NINA or PixInsight? Thank you.

[@CuivTheLazyGeek]

You can find the HFD in ASTAP as well - not FWHM though.

[@jfn480427]

Man, too much a medicine for this poor man...lol

[@CuivTheLazyGeek]

Hahaha, sorry!

[@KingLoopie1]

Uuuurrrtkkk! 🤮 Sigh.... Leave it to an engineer to over complicate things. There better be a program to do this for me or it ain't gettin done... (I still give the video thumbs up.) 😜👍

[@andrewwareing7291]

That made me dizzy!

[@CuivTheLazyGeek]

Sorry about that! :D