11 replies to this topic

[dale wilson]

I have a WO Megrez 90 doublet, I use for ap.

Would there be any noticeable difference shooting through a 115 triplet?  

 

Thanks in advance. 

[Sacred Heart]

To me,  it comes down to your eye, how well is the doublet corrected,  Assuming you are asking about the AT115EDT. Again to me,  just because it is a triplet does not make it better, in reality. Theoretically maybe, lots of good doublets out there.

 

What type of difference are you asking about??   FOV is slightly smaller in the AT115EDT,  The AT115EDT is larger / heavier, so now your mount is in question.

 

There are good doublets out there as well as good triplets,  imaging is also about processing.  There are a lot of great magicians out there and you may be one of them.

 

Just me saying,   Joe

[CHASLX200]

It would be a good jump up from 90 to 115mm.

[Skywatchr]

I have a WO Megrez 90 doublet, I use for ap.

Would there be any noticeable difference shooting through a 115 triplet?  

 

Thanks in advance. 

If your mount is up to the task, why not jump to a 122mm Triplet?  Here is an example of the beautiful images you can get once you "tune in" the back spacing.  Plus you get more resolution with either the 115mm or 122mm than you get with the 90mm.  So either way it is a step up.

 

https://www.cloudyni...ota/?p=13270910

 

I own one of these 122mm and it is an extremely nice scope.  And visually there is no CA whatsoever that I can see.

[Jon Isaacs]

If your mount is up to the task, why not jump to a 122mm Triplet?  Here is an example of the beautiful images you can get once you "tune in" the back spacing.  Plus you get more resolution with either the 115mm or 122mm than you get with the 90mm.  So either way it is a step up.

 

https://www.cloudyni...ota/?p=13270910

 

I own one of these 122mm and it is an extremely nice scope.  And visually there is no CA whatsoever that I can see.

 

It is a 122mm FPL51 Triplet, chromatic aberration is there... 

 

The Megrez 90 is an FPL-53 doublet with a focal length of about 560mm,   At least mine does.  These were mislabeled at the factory as having a focal length of 621mm..

 

Small step ups in aperture depend on the mount...  

 

Jon

[Skywatchr]

It is a 122mm FPL51 Triplet, chromatic aberration is there... 

 

The Megrez 90 is an FPL-53 doublet with a focal length of about 560mm,   At least mine does.  These were mislabeled at the factory as having a focal length of 621mm..

 

Small step ups in aperture depend on the mount...  

 

Jon

Perhaps technically, but I saw zero CA on Venus low on the horizon.  That was with the FF and a Nagler 5mm.  You just gotta see it to believe it.

[Jon Isaacs]

Perhaps technically, but I saw zero CA on Venus low on the horizon.  That was with the FF and a Nagler 5mm.  You just gotta see it to believe it.

 

With Venus low on the Horizon you should be seeing atmospheric dispersion.. what phase was Venus?

 

 

Jon

[Skywatchr]

 

With Venus low on the Horizon you should be seeing atmospheric dispersion.. what phase was Venus?

 

 

 

Jon

 

Maybe a little larger of a crescent, but close to that.  A bit higher up enough to clear the trees which helped. Plus the seeing was quite steady.  All the way to the edges of the Nagler 5 was clean as a whistle. I did not expect it, but there it was. The same with the SVBONY SV215 3-8mm Zoom.  Like I said, you gotta see it to believe it. There was a TAK 100 Fluorite Doublet practically right beside it, that did show some color, but nothing as bad as your photo..

[Kevin_A]

I have a WO Megrez 90 doublet, I use for ap.

Would there be any noticeable difference shooting through a 115 triplet?  

 

Thanks in advance. 

I would go up to 130-140mm. I have a 80mm and a 115mm and the difference is nice, and I think my 115mm would be better than the Svbony 122mm just because of what I have seen imaging wise so far. But if it is cost related then an Askar 140APO would give you a big boost in aperture for the buck over your 90mm if your mount is capable. 

[dale wilson]

To me,  it comes down to your eye, how well is the doublet corrected,  Assuming you are asking about the AT115EDT. Again to me,  just because it is a triplet does not make it better, in reality. Theoretically maybe, lots of good doublets out there.

 

What type of difference are you asking about??   FOV is slightly smaller in the AT115EDT,  The AT115EDT is larger / heavier, so now your mount is in question.

 

There are good doublets out there as well as good triplets,  imaging is also about processing.  There are a lot of great magicians out there and you may be one of them.

 

Just me saying,   Joe

I am using a Celestron CGX-L mount.  I don't have any problem with weight.  So, what I am looking for is resolution and color correction.

Is the resolution going to be apparent enough in the ap side to make the change worth the effort?  Or, would a 120 (or bigger) be needed to be noticeable?

I, mostly, shoot deep sky.  Does the triplet affect the color of the stars, as opposed to a doublet?

 

The Megrez 90 is my first refractor, used for ap.  I think it has been a great ota.  Trying to justify moving up.

 

Thanks again for all the insight.

Edited by dale wilson, 22 February 2024 - 01:04 PM.

[Sacred Heart]

I am using a Celestron CGX-L mount.  I don't have any problem with weight.  So, what I am looking for is resolution and color correction.

Is the resolution going to be apparent enough in the ap side to make the change worth the effort?  Or, would a 120 (or bigger) be needed to be noticeable?

I, mostly, shoot deep sky.  Does the triplet affect the color of the stars, as opposed to a doublet?

 

The Megrez 90 is my first refractor, used for ap.  I think it has been a great ota.  Trying to justify moving up.

 

Thanks again for all the insight.

Dale,

 

My opinion,  a 120 - 140 would be a considerable jump, both visual and imaging.  However with imaging it will be more demanding on your mount. Size, focal length and weight play a role in imaging / tracking / guiding.  Not to say the CGX-L cannot handle it, it should.  Also, your camera, you may want a larger chip, I did. I'm getting a 130mm f8 refractor, 1040m focal length.   For my 130 I'm getting an OAG to guide with.

 

Do you plan to image at 900mm, a 120mm or 140mm scope with no reducer - just flattener, image scale is .9 or less. with a .7 reducer image scale is 1.2 which is a little more manageable. Either way you guiding error needs to be lower than the image scale.

 

Color correction is a sticky story, this depends on how well the lenses were ground and aligned.  That can vary on any scope, especially a massed produced scope.

 

There are people here who could tell you about color correction a lot better than me.  I hope they chime in.

 

I may have said this earlier, there are APO's that are doublets and there are APO's that are triplets.  My TV76 I believe is a doublet, my CFF92 is a triplet, my Agema 130 f8 is a doublet.

 

I believe that color correction depends on the glass, how well it is made, ground and assembled. 

 

In general, yes - I believe you would be happy going to a 120 - 140 class scope.  Get you a good one.   Warning, speaking of refractors, with good glass up front -  it demands good glass in back.  Eyepieces.  I had to upgrade mine.

 

Good luck,     Joe

[CHASLX200]

Nothing like seeing a boiling rainbow Venus when it is low,