9 replies to this topic

[Goyen]

I recently got an Esprit 120ED and paired it with the included SW field flattener and my Nikon Z6ii.  Shot a first light test of Capella and got sharp stars, but the corners weren't perfect.  I over-processed this to really show the vignette and weird colored rings in the corners (this is one light, 30sec, ISO3200, no stacking/flats):

 

 

 

I checked in Siril and got the below result for distortion/tilt:

 

 

 

Distortion wasn’t terrible but I didn’t like the corners, so I measured backfocus more carefully and noticed it was ~76-77mm instead of 75mm.  I adjusted the variable extension tube and got to exactly 75mm.  Did another test a few nights later, shooting M51.  Again this is a single light (120sec, ISO1600), similar over-processing as the Capella shot:

 

 

 

The rings and vignette got noticeably worse. Measuring distortion again in Siril:

 

 

 

Here is the setup between the field flattener and the camera.  20mm empty filter holder + 39mm extension tubes + 16mm from camera flange to sensor = 75mm:

 

 

 

How should I be dialing this in?  Is this an issue with my extension tubes?  Or the flattener?  I thought I just had to hit 75mm, but I feel like I’m doing something wrong.  Any help would be awesome, thanks.

[skyward_eyes]

If you are using the M48 threads, which you are in the picture, the back focus is 55mm. You need to trim about 20mm out of your train. 

[Goyen]

If you are using the M48 threads, which you are in the picture, the back focus is 55mm. You need to trim about 20mm out of your train. 

Will try that, thanks!

 

I took a cleaner picture of my existing setup + measurements.  Is the 75mm from the instruction manual for non-full frame cameras only?  Or for using filters?

 

 

 

 

 

[Kevin_A]

Will try that, thanks!

 

I took a cleaner picture of my existing setup + measurements.  Is the 75mm from the instruction manual for non-full frame cameras only?  Or for using filters?

 

 

 

 

 

The only issue I see is the small looking diameter t-ring and svbony spacer. That might account for the vignetting if they are not M48 spacers and t ring. The 75mm should be correct.
Not sure why anyone would say 55mm backfocus as backfocus is 100% based on the flattener requirement which is for sure 75mm.  My Esprit 100ED is 63mm but comes with an included 8mm spacer so I can use standard spacers that easily equal 55mm. 

Edited by Kevin_A, 24 April 2025 - 12:05 PM.

[Kevin_A]

You may have much better results using a more standard approach like I do when using my Nikon Z7 on my Esprit. 

I simply use my Nikon Z7 with the FTZ adapter which has a bigger opening thus reducing vignetting and that combined is 46.5mm… and then I attach a standard F mount Nikon M48 T-Ring adapter which is 8.5mm thick. That stack of those parts equals 55.0mm to which you thread that onto your 20mm thick spacer that is screwed onto the flattener. Thus a better 75mm. Cheers!

 

here is how it will look. Screw this onto your 20mm adapter and all will be good.

 

 

Adapter is a standard Nikon M48 T-Ring adapter for F lenses… it works on typical D5300, D850 cameras and fits the FTZ adapter perfectly. The reason you should use a FTZ is because it has a rectangular opening inside that allows fullframe illumination without vignetting and distortions. 

Edited by Kevin_A, 24 April 2025 - 12:54 PM.

[Kevin_A]

Fyi…. Do not rely too heavily on tilt numbers from Siril. Rely more on the star quality in the corners. 
Siril tilt numbers can sometimes be erroneous but a lot of tilt can be just from the t-rings being sloppy which is not uncommon.

[skyward_eyes]

Ah, ok your set up is correct as you have it. 

 

Looking at your images, as Kevin A has also mentioned, look at your images and how the stars look. When I look at just the images your stars look fine, at least from what CN will allow you to post resolution wise. 

 

You can get into the weeds really quickly with this stuff but ultimately it comes down to the image. Does your image look good? If yes, then just go with it. Software testing is made to show issue, but the question is, how big of an issue is it actually? 

[Kevin_A]

Here is a image of the FTZ adapter and see how the end that goes onto the camera needs a big rectangular opening to clear the fullframe sensor corners. 
cheers!

 

that is why I only use my nikon z7 with the nikon FTZ adapter for spacing….. and it works beautifully on my Esprit and Askar fullframe compatible scopes. The z7 bayonet is almost 55mm so you can see how big the rectangle is… at least 48mm diagonal corner to corner. Cheers! 

Edited by Kevin_A, 24 April 2025 - 01:12 PM.

[Goyen]

The only issue I see is the small looking diameter t-ring and svbony spacer. That might account for the vignetting if they are not M48 spacers and t ring. The 75mm should be correct.
Not sure why anyone would say 55mm backfocus as backfocus is 100% based on the flattener requirement which is for sure 75mm.  My Esprit 100ED is 63mm but comes with an included 8mm spacer so I can use standard spacers that easily equal 55mm. 

 

I hadn't thought about the diameter of the tubes! I'm using the svbony variable tube and a 5mm ring from this other set. They are connecting into a Baader S52 / M48 inverter ring which is secured in the Baader Wide T Ring connected to the camera.

 

 

 

You may have much better results using a more standard approach like I do when using my Nikon Z7 on my Esprit. 

I simply use my Nikon Z7 with the FTZ adapter which has a bigger opening thus reducing vignetting and that combined is 46.5mm… and then I attach a standard F mount Nikon M48 T-Ring adapter which is 8.5mm thick. That stack of those parts equals 55.0mm to which you thread that onto your 20mm thick spacer that is screwed onto the flattener. Thus a better 75mm. Cheers!

 

here is how it will look. Screw this onto your 20mm adapter and all will be good.

 

 

 

Adapter is a standard Nikon M48 T-Ring adapter for F lenses… it works on typical D5300, D850 cameras and fits the FTZ adapter perfectly. The reason you should use a FTZ is because it has a rectangular opening inside that allows fullframe illumination without vignetting and distortions. 

 

 

I actually own the FTZ adapter already, so I tried this after reading your post.  I also own this Celestron t-ring for F-mount (got it a few years ago to attach my camera to someone's telescope).  Unfortunately, the threading on that Celestron ring was not M48, and the ring was too small to fit the Baader S52 / M48 inverter ring.

 

Which brand of F-mount t-ring are you using?  I see William Optics makes one that looks similar.

 

 

Fyi…. Do not rely too heavily on tilt numbers from Siril. Rely more on the star quality in the corners. 
Siril tilt numbers can sometimes be erroneous but a lot of tilt can be just from the t-rings being sloppy which is not uncommon.

 

Interesting, I will keep this in mind, thanks!

 

 

Ah, ok your set up is correct as you have it. 

 

Looking at your images, as Kevin A has also mentioned, look at your images and how the stars look. When I look at just the images your stars look fine, at least from what CN will allow you to post resolution wise. 

 

You can get into the weeds really quickly with this stuff but ultimately it comes down to the image. Does your image look good? If yes, then just go with it. Software testing is made to show issue, but the question is, how big of an issue is it actually? 

This is a valid point.  The stars don't look bad, I'm just not very experienced and wasn't sure if I was using the field flattener correctly because of Siril's red lines.

 

 

 

Here is a image of the FTZ adapter and see how the end that goes onto the camera needs a big rectangular opening to clear the fullframe sensor corners. 
cheers!

 

 

that is why I only use my nikon z7 with the nikon FTZ adapter for spacing….. and it works beautifully on my Esprit and Askar fullframe compatible scopes. The z7 bayonet is almost 55mm so you can see how big the rectangle is… at least 48mm diagonal corner to corner. Cheers! 

 

Looking forward to trying it, thanks!

[Kevin_A]

I hadn't thought about the diameter of the tubes! I'm using the svbony variable tube and a 5mm ring from this other set. They are connecting into a Baader S52 / M48 inverter ring which is secured in the Baader Wide T Ring connected to the camera.

 

 

 

I actually own the FTZ adapter already, so I tried this after reading your post.  I also own this Celestron t-ring for F-mount (got it a few years ago to attach my camera to someone's telescope).  Unfortunately, the threading on that Celestron ring was not M48, and the ring was too small to fit the Baader S52 / M48 inverter ring.

 

Which brand of F-mount t-ring are you using?  I see William Optics makes one that looks similar.

 

 

 

Interesting, I will keep this in mind, thanks!

 

 

This is a valid point.  The stars don't look bad, I'm just not very experienced and wasn't sure if I was using the field flattener correctly because of Siril's red lines.

 

 

Looking forward to trying it, thanks!

Get yourself an nikon t ring F mount adapter that is m48 on amazon and everything will be fine. They are super cheap. 

cheers.

 

https://www.amazon.c...aps,144&sr=8-1 

Edited by Kevin_A, 26 April 2025 - 08:30 AM.