Pinched optics and how to correct it

[@wildobson]

Hey Garnett. Thank you for being the ONLY person on KZbin who is talking about this directly. I recently cleaned my mirror for the first time, and found NO instruction on clip tightness in my product manual, so I assumed hand-tightened was proper. I ended up with quadruple images and point-light pinching (quadrupled again). Seeing your video and the number of clips you used helped me to determine it was my 4 over-tightened clips which were causing my inability to view properly at high magnification (10mm and smaller eyepieces). Well done sir!

[@GarnettLeary]

Hey glad it helped. Honestly I look for holes and gaps in information and try to fill them. There’s no point in reiterating topics that have been repeated millions of times. This particular issue was one I discovered while discussing mirror blank grinding with a friend whose very old school. I was rather stumped by it myself. I had for years discarded it as cheap manufacturing over an actual correctable problem. There’s so many aspects of this hobby, photography or visual, that can work heavily against you and discourage you. It’s no mystery why so many scopes end up in closets. When I get comments like yours it encourages me to continue thinking of these. The Jones collimation video seemed to be helpful also. There’s way too many people b-rolling and not truly offering help to people. As a community the folks into astronomy have endless amounts of information to share with one another. I feel it’s everyone’s responsibility to use the internet as a tool to reach folks who aren’t active in astro groups. It makes my day when someone tells me I was helpful. Thank you for watching and I’m glad you solved the issue. I don’t post regularly but I am transitioning into the guided aspects of astrophotography soon. My primary interest is reaching people who are just starting or on limited budgets. There’s a lot less hiccups that come with higher price tags but a whole lot less people interested in large investments into hobbies they aren’t sure they will like. We have endless amounts of information to share with one another to grow this community. Clear skies.

Yes even after 5 years of this upload you helped one more Newtonian owner. Thank you Garnett for fixing my triangle stars. 😃😃

[@GarnettLeary]

It was totally worth posting if only reached one person. I’m honored. Clear skies.

[@basisTermium]

Dude, You just help me figured out the problem that i have been searched for a year.Thank you so much!

[@GarnettLeary]

Glad it was useful. Thanks for watching. Clear skies.

[@WhiteCrowFarm]

You’ve got a great collection of videos! Lots of useful information. Thank you!

[@GarnettLeary]

Thank you. That’s very encouraging and if it’s useful it’s worth it. Clear skies.

[@bobbyzamora1668]

Thanks mate! You've saved a few days of my headache

[@GarnettLeary]

Thanks for watching

[@charlieself]

Thank you so much. I got a 2nd hand dobsonian. Mirror was really dusty. Watched few videos on how to clean but none told me about tightness of mirror clamps. I over tightened mine and had triangle stars. It's been 6 months since I did it and I have just taken mirror out. Unfortunately the edge of the mirror has shattered from the tightness, possibly made worse by the extreme temperatures my conservatory reaches where I have been storing it. I wish I had seen this before I did the damage. You live and learn I suppose. Waiting for cleaning supplies to arrive, I'll give the mirror a clean and put back in. Fingers crossed the shard missing from the edge won't impact the image I see. The shiny part of the mirror is still intact, its the edge down to the bottom that's chipped off.

[@GarnettLeary]

It shouldn’t degrade it. It may slightly effect it. Unfortunately the people selling scopes typically know little about them. Most everything is mass produced and lacking in instructions. This is one of those things most people overlook.

[@GalaxyArtMedia]

Good video Garnett!

[@AndreH3d]

thank you after 2 days of testing and ruling out issues I came across this video, I am almost sure my issues is pinched optics, because I tested backfocus spacers, filters and no filters, coma corrector and no coma corrector... collimated several times, I was reading about pinched optics and after a few reads I was sure thats the issue and went to search a video that shows how to fix this, so Tahnk you, I will work on this now and try to get it working, too bad clouds are rolling in and will not be able to test this further tonight

[@GarnettLeary]

Thanks for sharing. It is one of those things that’s widely overlooked. It drove me crazy once. I didn’t want it to happen to anyone else. The bigger the mirror the more crucial that gap is.

[@AndreH3d]

@@GarnettLeary and indeed it was pinched optic! my stars are much better now... have some coma but not sure where to look at now... one step closer though!

[@GarnettLeary]

Do you have a corrector?

[@KENNGODD1]

Very informative, much appreciated and Clear Skies

[@GarnettLeary]

Same to you. Thanks for watching.

[@GalaxyArtMedia]

Nice video mate!. Good info!

[@twigle3015]

Thank you for this! This is tremendously helpful for me

[@GarnettLeary]

I’m glad. Thanks for watching. Clear skies.

[@indoguju]

Great video thanks

[@GarnettLeary]

Thanks for watching. Clear skies.

[@irfanrashid2114]

Hi! Did you change the center spot of your mirror? Aren't you afraid of credit card scratching the mirror surface? Btw you have a really nice channel. Great work! I am a subscriber now.

[@GarnettLeary]

I didn’t change the center dot but it’s a real good idea to check it and make sure it’s correct. I always use a card. Never had a problem. I’m not adding any direct pressure and it’s relatively flat. Pinching glass is one of those things that can throw you way off. The center will usually be fine. It’s hard to diagnose on a new scope because the glass itself may have the stigmatism. Thank you. I try to post things and topics that are useful. Thank you for subscribing. I hope you stick to the hobby. Clear skies.

[@chrisfleming7531]

Good to know man thank you

[@ADRIANNORMANNINA]

Waw, that's realy good to know

[@AB-ft2lb]

Do you know how to square a focuser in a tube?

[@GarnettLeary]

The easiest way I know to do it is by adding washers between the focuser and inner wall of the tube. In theory you can use a laser collimator or collimation cap to sight thru. A white piece of paper, folded to find center, and placed in front of the objective serves as a guide. This is very practical and easy to do.

[@GarnettLeary]

Alternatively teflon tape works really well to snug a focuser that is sloppy all way round.

[@AB-ft2lb]

@@GarnettLeary Thanks, gonna give it a try

[@GarnettLeary]

Some folks use shims of different materials. I’ve seen an Astroscan perfectly collimated using small strips of electrical tape on the threads. A section of a styrofoam cup might work. Be creative. The main thing is to establish the center and work from it. If you have a removable dew shield consider taking it off. If you align off of it, the shield itself may not be seated square to the lens.

[@lajoswinkler]

I have just one complaint. You placed a credit card on a visibly dirty primary mirror and wiggled it around pressed against it. Dirt is always harder than the metal coating and that action _will_ scratch it. Primary mirror should never be touched dirty. Only clean, and then only with something soft like a piece of rice paper.

[@GarnettLeary]

Can’t disagree with your logic. Excellent points and very true.

[@dedskinprodcerdj4273]

youll brake ppls telescopes , but non the less i will tray it , i didn't notice anything wrong with stars if they are in focus but i did notice as i focus they get smaller and triangular as they go small , but if you ask me that is under or over focused , when its spot on all is ok.

[@GarnettLeary]

What type of telescope do you use?

[@dedskinprodcerdj4273]

as shown , reflector 4,5inch 500mm