Platesolve failuer by SkyWatcher Mak90 with extender barrel

tobosaku

Hello

Please give some advice.

My equipments.

ASIair Pro

Telescope--Skywatacer Mak90 f=1250mm

Camera -- CanonEosX7i(7000D)

I succeeded PlateSolve in this combination.

But in this combination, the field of view is limitted.

So I added 50mm extender barrel.

Then, The focal length seems to extend a little.

I estimated the focal length to be about 1450mm by comparing and calculating the images taken on trial.

So I tried while changing the focal length step by step,from 1400mm to 1500mm.

But I can't.

Asiair recognized hundreds of stars,but PlateSolve failed.

How can I do?

w7ay

I don't quite understand what you are trying to do, are you trying to widen the field?

If there are more stars after you have inserted the extra extender, the focal length of your optical system should have become shorter, not longer (1450mm) as you have mentioned. Try adjusting your plate solve the other way -- use focal lengths that are shorter than 1250mm.

I don't know about the Maksutov that you are using -- did they specify a back-focus for imaging? If so, adding the extender can cause other problems, like field flatness problem, or even the sensor plate no longer becomes gnomonic tangent planes. The latter will cause star asterisms to change shape and you lose ability to plate solve (especially near the poles).

You can also take an image, save it and upload it to astrometry.net and let it plate solve for you. If astrometry.net cannot match a plate, the star field has sufficient geometric distortion that pretty much no other plate solver could do it. It should give a plate scale in the results window. You then use the plate scale and the sensor's pixel size to compute the focal length of your system.

Try for between 24 and no more than 200 detected stars. Too many stars would just make it more difficult to plate solve (unless the program is set up to reject dimmer stars to being with). The other key to plate solving is to never let the stars saturate. The Max ADU of your plate should not get above 60000.

Clear skies

Chen

tobosaku

Thanks for your advice.

SkyWatcherBkMak90 has a small image circle, so if I directly connect my EOS, the image surroundings is missing.

Then, attach a 50 mm extension tube (just a cylinder, no lens) , this problem is solved, but the size of the image become slightly larger.

I don't know why.

I tried to calculate the focal length with astrometry.net but it didn't work. The image used may not have been appropriate. When it comes to a nice night, take another test image and try again.

Thank you very much.

PMTeam@ZWO

tobosaku wrote:

Thanks for your advice.

SkyWatcherBkMak90 has a small image circle, so if I directly connect my EOS, the image surroundings is missing.

Then, attach a 50 mm extension tube (just a cylinder, no lens) , this problem is solved, but the size of the image become slightly larger.

I don't know why.

I tried to calculate the focal length with astrometry.net but it didn't work. The image used may not have been appropriate. When it comes to a nice night, take another test image and try again.

Thank you very much.

You can try to reduce the ISO or enter 0 into the FL box let the ASIAIR to cacl it. BUT as you said if the astrometry.net did not work, there must be something wrong about the image, too much noise? If you can, please share your astrometry.net task to us, we can try to PS your image too.