12 replies to this topic

[forestgunp9]

Hi
I have a monochrome setup, asi2600mm without tilt(12.5mm bf), Efw 7x36mm(20mm bf), oag-l(17.5mm bf), 7.5mm extensors, and Baader MPCC Mark 3 Coma Corrector(57.5mm backfocus).
7.5mm between oag-l and Coma Corrector.
What can I do with my new Wanderer lite V2 10mm profile field rotator I'm waiting for? Sell it?
Change the coma corrector?

[triplemon]

Use a mount that doesn't necessitate a field rotatior ?
Test first if 2.5mm more BF changes performance more than you want ?
Literally "shave off" a few mm somewhere and e.g. replace a threaded interface by a direct glued one ?

 

I even wonder how you'll make OAG work with the field rotator ? As the field rotator will rotate around a different centroid than what the OAG guides on, so you'll have a nifty problem to solve regardless of the OAG being in front or behind the rotator.

Edited by triplemon, 11 November 2024 - 02:13 PM.

[forestgunp9]

Hi.
First, sorry for my English.
Second, I have to say I'm a real beginner with only one nebula picture up today. It's was cropped by Pixinsight a lot.
I bought this field rotator, because I want to set the same field for lights from consecutive nights, a filter by night.... SHO, and lrgb one more night.

I thought a field rotator was the best way to do that, to fit the last night field, and continue the process.
I understood all you say but the last one about oag and field rotator?

[triplemon]

I dont think you understand what a field rotator would do for you - and what it can not do.

If your have an equatorial mount and don't disassemble scope and camera, the image will not be rotated the next day or even a month or ten years later.

If you do take down the scope or otherwise accidentially rotate the camera, a field rotator wont help youto return the cameta to the exact rotation as it was before, so the images line up exactly.

And even if it would, it would not make your flates perfectly valid for the images takes a bit later. Much of the imperfections is dust on the sensor and that one moves overtime. Surely when you take off the camera. And even if the duat does not move - it rotates with the camera. .. so at the end, most imperfections that you correct with flats all relate to the camera itself. The optical path in front of the rotator is symetric enough that rotating the camera wont change the validity of the flats.

Edited by triplemon, 11 November 2024 - 09:40 PM.

[psandelle]

First, a rotator (I assume you’re using it on an EQ mount to frame your image and not on an Alt/Az mount to derotate your image) is exactly the tool to frame an object one night, then reframe it exactly the same the next night, or the next week, or the next year (especially if you have software to automate it like Voyager, or NINA, etc.; though you can do it manually, too). And if you do two different images in a night, you can frame your lights for each image as well. So, you have the right tool.

 

The problem is finding those extra 2.5 or so millimeters. You could find a thinner OAG (there are some that are 10 to 12 mm thick, if memory serves). You could use a guide scope instead of the OAG, but without knowing the focal length/type your telescope is, that may or may not be advisable. You might find a different coma corrector, but a lot of them are scope dependent and tend to be the same BF.

 

Thats about all I can think of at the moment.

 

Paul

Edited by psandelle, 11 November 2024 - 11:28 PM.

[forestgunp9]

Yes, that's what I will try to do, reframe next nights with Nina and a picture from previous night.
I have a iOptron Gem45 mount, a newtonian OOUK CT8 F4.5 (900mm FL).
I was searching, and think I can change coma corrector, to get those 2.5mm.
I don't want to add more weight to the mount with a new telescope for guiding and a the actual dovetail I have, to fit the guide telescope on, it's big and heavy too.
My actual coma corrector needs 57.5mm bf, and I could see, there are some ones 60mm and more BF, as Televue for example.

My problem was my first images was crop by Nina because of field rotation between sessions...

[forestgunp9]

I meant the images was cropped by Pixinsight, not Nina

[psandelle]

Yes, that's what I will try to do, reframe next nights with Nina and a picture from previous night.
I have a iOptron Gem45 mount, a newtonian OOUK CT8 F4.5 (900mm FL).
I was searching, and think I can change coma corrector, to get those 2.5mm.
I don't want to add more weight to the mount with a new telescope for guiding and a the actual dovetail I have, to fit the guide telescope on, it's big and heavy too.
My actual coma corrector needs 57.5mm bf, and I could see, there are some ones 60mm and more BF, as Televue for example.

My problem was my first images was crop by Nina because of field rotation between sessions...

If changing the coma corrector can get you the extra milometers and not ruin any FOV or edge performance, then I think you have the perfect answer. Double-check they work with that scope, though!!!!

Paul

[forestgunp9]

I will left oag and move to a guiding telescope....

[Dan_I]

My actual coma corrector needs 57.5mm bf, and I could see, there are some ones 60mm and more BF, as Televue for example.

 

This would be the best solution because the MPCC does not perform well below f/5, so you'd not only solve your backfocus problem but also improve image quality.

[forestgunp9]

I just bought a skywatcher evoguide 50mm for guiding without oag-L.
But in the while, I will try putting the rotator between coma corrector and oag-L. That turn distance to sensor to 62mm ...
57.5(actual bf) - 7.5(tube extensions) + 10mm(rotator) + 2mm( m54 to m48 adapter) = 62mm

[forestgunp9]

Rotator arrive this week, evoguide arrive in 2 or 3 weeks

[chvvkumar]

I am late to this but I also use an EFW with an OAG. Check if your reducer has any removable elements. Mine for the 140 APO has a removable 18mm piece that exposes an M54 female thread I intend to fill up with the same rotator. Here is my calculation after I remove the 20mm adapter from the reducer