XLT120 f/8.3 coatings

[Ben Cartwright SASS]

I have a XLT120 that I bought for $125 (with CG4 mount) at a pawn shop. It was missing a few pieces on the mount and the diagonal was busted but it seemed ok, got it about 3 years ago.

I have no idea what the coatings were or if they were ok or not. ANYHOW I had it covered out back about 2 years ago with a Telegizmo cover, during a wind and rain storm it blew off (not the covers fault I didn't cinch it down) and the scope got a couple cups of water inside it, when I rotated it the water poured out of the dew shield! I could see the water between the cells, it was half covered (lower half), looked cleaner than the upper half.
I sent it to a scope shop in NH to have the cell dissembled and cleaned (didn't think about the coatings) now I compare the shots with that scope to my XLT102 or my SW 100 or the new Lunt ED102 and it is not as sharp as the other scopes even the cheap XLT102 f/6.4

How can I tell if the coatings were compromised or even still there?

[bladekeeper]

I am wondering, Jeff, if the lack of sharpness is due to improper alignment of the crown and flint after reassembly.

The coatings should be fairly obvious on the glass if the right light source at the proper angle is shined upon them.

This would be a good thread for JG, Gabrielle, or nFA to chime in on...

[Bigzmey]

I just checked my XLT150 and if you remove dew shield and look at angle you will see purple tone. I would also do star test to see if it is properly collimated.

[notFritzArgelander]

I wouldn't worry about the coatings. They are certainly NOT water soluble or reactive with water. There might be some residue left from evaporation... But I would mostly worry about collimation.

I had one of these OTAs about 10+ years ago and out of the box I thought it was a tad soft optically. So I used my artificial star and collimated the thing, optimizing the rotation of the two lenses and it was a jim dandy scope after that. There was an opposition of Mars in Aug 2003 and the volcanos on Tharsis were just so pretty in it! Olympus Mons and the three littler guys just snapped.

It was a terrific planetary scope thereafter.

[Ben Cartwright SASS]

Thanks guys, I will check collimation

Did you guys see my comparison between the 102 f/7, 100 f/9 and the XLT120 f/8.3? I shot those at 11 am and the air was very unstable (although I have seen it worse) so wonder if the longer focal length makes a difference to some degree. The 120 isn't "bad" but not as tack sharp as the Lunt ED102 of course the XLT is regular glass and the ED102 is FPL51 or 53 or something much better glass and that can make a difference also.
The shots are from Astrostakkert with their sharpening, I will be working them today with the regular way I do images to see what we get.

I guess it is I want my Jeep to drive like a Ferrari

[Bigzmey]

The shots look pretty good. I don't do AP but visually APO/ED scopes do deliver sharper views to my eyes than achros.

[notFritzArgelander]

Did you guys see my comparison between the 102 f/7, 100 f/9 and the XLT120 f/8.3? I shot those at 11 am and the air was very unstable (although I have seen it worse) so wonder if the longer focal length makes a difference to some degree. The 120 isn't "bad" but not as tack sharp as the Lunt ED102 of course the XLT is regular glass and the ED102 is FPL51 or 53 or something much better glass and that can make a difference also.
The shots are from Astrostakkert with their sharpening, I will be working them today with the regular way I do images to see what we get.

No I didn't see that comparison. Could you indicate where it is?

Longer focal length is not a factor in poor seeing. Larger aperture is more sensitive to seeing issues. It's a bit of a simplification but the characteristic length of turbulent eddies in the atmosphere makes seeing worse for larger apertures. That's why aperture masks work to improve seeing while the focal length remains the same.

[Gordon]

Did you guys see my comparison between the 102 f/7, 100 f/9 and the XLT120 f/8.3? I shot those at 11 am and the air was very unstable (although I have seen it worse) so wonder if the longer focal length makes a difference to some degree. The 120 isn't "bad" but not as tack sharp as the Lunt ED102 of course the XLT is regular glass and the ED102 is FPL51 or 53 or something much better glass and that can make a difference also.
The shots are from Astrostakkert with their sharpening, I will be working them today with the regular way I do images to see what we get.

No I didn't see that comparison. Could you indicate where it is?

Longer focal length is not a factor in poor seeing. Larger aperture is more sensitive to seeing issues. It's a bit of a simplification but the characteristic length of turbulent eddies in the atmosphere makes seeing worse for larger apertures. That's why aperture masks work to improve seeing while the focal length remains the same.

Here's the link: viewtopic.php?f=73&t=439&p=4049#p4049

[notFritzArgelander]

Did you guys see my comparison between the 102 f/7, 100 f/9 and the XLT120 f/8.3? I shot those at 11 am and the air was very unstable (although I have seen it worse) so wonder if the longer focal length makes a difference to some degree. The 120 isn't "bad" but not as tack sharp as the Lunt ED102 of course the XLT is regular glass and the ED102 is FPL51 or 53 or something much better glass and that can make a difference also.
The shots are from Astrostakkert with their sharpening, I will be working them today with the regular way I do images to see what we get.

No I didn't see that comparison. Could you indicate where it is?

Longer focal length is not a factor in poor seeing. Larger aperture is more sensitive to seeing issues. It's a bit of a simplification but the characteristic length of turbulent eddies in the atmosphere makes seeing worse for larger apertures. That's why aperture masks work to improve seeing while the focal length remains the same.

Here's the link: viewtopic.php?f=73&t=439&p=4049#p4049

Thanks Gordon. Since the comparison is done on daytime images when seeing is particularly bad it's not surprising that the 120mm aperture would have more problems. Again, as I commented on the original thread, seeing affects aperture not focal length. So a drop off, especially in the daytime, between 100 and 120mm aperture is not unusual.

One can partially hide the effects of poor seeing by using a lower magnification (or shorter focal length at prime focus) or an aperture mask. Aperture masks mitigate atmospheric seeing problems without changing the focal length of the scope.

[Lady Fraktor]

I cannot add much to what nFA has stated, I would check the focuser alignment and objective collimation.
The last 102mm I refurbished was found laying in a earthen floor shed in a puddle of dirty water and the lens cleaned up very well so I would imagine yours should be alright.