8 replies to this topic

[tocster]

So I recently picked up a second hand Esprit 120, and it came with the 0.77x focal reducer.  While the specs say it should have a backfocus of 55mm (with the included spacer) Im finding that even at about 61mm it is giving me stretched stars in the corner of an APSC sensor.  Im still experimenting with it, but wanted to check in if others have noticed this?

 

 

I have attached an example from NINA - its actually not terrible I guess, but I suspect this would be poor on a full frame sensor.

 

 

 

Attached Thumbnails

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Edited by tocster, 28 May 2024 - 06:17 AM.

[tocster]

So I did some experimenting tonight - I added additional 10mm of backfocus, and was right at the limit of the focuser - I'm using the guide here:

 

https://optcorp.com/...rect-back-focus

 

I was not able to get the star images to resemble the 'sensor too far way' pattern.  They always seem to appear pointing towards the centre of the image, no matter what I do 

 

btw this is the spacing set to 55mm - Im wondering if my issues are just tilt?

Attached Thumbnails

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Edited by tocster, 28 May 2024 - 07:13 AM.

[gpom]

I bought my Esprit 120 new and bought the 0.77x reducer used from the classifieds. I never was able to get good stars from it and did the exact same thing as you, in fact my stars looked almost exactly the same as yours. I then bought a new reducer from Skywatcher and was able to get almost perfect stars with 56mm of back focus (using 1mm thick filters so added an additional 1mm). So based on my experience, I'd say you have a bad reducer and your options are either buy a new one or use the scope at native focal length. And as an aside, using a reducer will always impact the quality of the stars. How much depends on your tolerance, I'm not looking for 100% perfect, just good enough.

[Kevin_A]

Add more until they stop being elongated. Since they look even there is no tilt. Nothing to lose. 
I have the 100ED and it is perfect. My backfocus is 63mm stock but the scope comes with an 8mm spacer to give me 55mm to fill. 

[freeme62410]

So I did some experimenting tonight - I added additional 10mm of backfocus, and was right at the limit of the focuser - I'm using the guide here:

 

https://optcorp.com/...rect-back-focus

 

I was not able to get the star images to resemble the 'sensor too far way' pattern.  They always seem to appear pointing towards the centre of the image, no matter what I do 

 

btw this is the spacing set to 55mm - Im wondering if my issues are just tilt?

Just so you know bud, that tab under imaging that says "abberation inspector" will have you run an autofocus and tell you exactly how much tilt and backfocus error you have, and exactly which direction it is in. It looks to be too close, but the inspector will tell you for sure. And no that is not just tilt. that is backfocus error.

Edited by freeme62410, 29 November 2024 - 04:50 PM.

[Drothgeb]

I use the Explore Scientific 0.7x with my Esprit 150. Not perfect, but works pretty well.

[astrobug BE]

A friend of mine use this reducer with great succes on his esprit 120:

 

https://www.teleskop...vollformat-5120

 

I had no idea the SW reducer are so bad

Edited by astrobug BE, 30 November 2024 - 09:36 AM.

[crackout]

I had the same issues with the .77x SW reducer so I sold it right away. However, the M63 Riccardi works perfectly (APSC).

Edited by crackout, 30 November 2024 - 11:27 AM.

[lviatour]

I have a SkyWatcher Esprit 120ED and a 0.77x reducer. I'm working in full-frame 24x36 format and I'm not having any issues, just slightly less quality in the extreme corners.
 

Here are some examples I've taken with the reducer:

 

 

 

Here's how I achieve the 55mm backfocus and the same setup for 55mm with the original corrector:




 

Edited by lviatour, 04 December 2024 - 03:17 AM.