R.A. finder cross hairs too thick (SOLVED)

[Space Cowboy]

I recently purchased a 9x50 astro essentials right angle findersope from FLO to replace my Skywatcher 9x50 straight through findersope. 

Tried the right angle findersope last night and the cross hairs appear way too thick completely obscuring Venus in the evening sky. The optical train is much shorter from the crosshair so I assume this is why it appears thicker.

Does the right angle Skywatcher findersope have the same issue? Do I have to look for a much more expensive replacement? For planetary imaging the astro essentials finder is no use with such coarse crosshairs.

SOLVED!

Sent the AE finder back and got this as replacement. Not tried on scope yet but crosshairs are nice and fine! Only 10 quid more and comes with a shoe! Looks far better quality.

https://www.firstlightoptics.com/finders/stellalyra-8x50-right-angled-correct-image-raci-finder-scope-with-bracket.html

 

Edited March 16, 2023 by Space Cowboy

[michael8554]

Hi Stuart

The cheap but irritating solution would be to slightly defocus.

Until Venus appears as a circle slightly larger than the crosshairs.

Michael

[Space Cowboy]

Unfortunately I need to be more accurate than that when centering a planet at f20 on a camera chip 🙂

[michael8554]

If splitting a slightly defocused Venus on the crosshairs isn't accurate enough, you need a Flip Mirror.

Michael

[Space Cowboy]

1 hour ago, michael8554 said:

If splitting a slightly defocused Venus on the crosshairs isn't accurate enough, you need a Flip Mirror.

Michael

The cross hairs are so thick it would have to be more than slightly defocused. In over 10 years of planetary imaging I've always found a sharply focused findersope easier to accurately align. Fainter targets like Saturn and Polaris would be hard to see if not in focus especially on a hazy night or if there was some dew on the optics.

[mikeDnight]

It may be an expensive option but you could use a 50mm guide scope with an interchangeable eyepiece, and use a guiding eyepiece or astrometric eyepiece. Or use a Takahashi 50mm finder which have a very fine illuminated reticule, but they view straight through.

[Paz]

Some finders have  pairs of parallel lines that cross over forming a tiny box in the centre so you can see the object dead centre. Some of my finders are like this, if my memory is correct I think I got these from Orion (the USA company).

[Space Cowboy]

Thanks MikeDnight and Paz for those ideas. To be honest i'm trying to keep costs down but its always interesting to hear different suggestions.

Edited February 27, 2023 by Space Cowboy

[Mr H in Yorkshire]

It may not be possible for you for whatever reason, but I once had a similar problem and was able to replace the crosshairs with actual spider silk. I marked 90 degree intervals on the metal rim to guide the placement and as I remember, used shellac to fix the threads on the rim. It actually worked too.

[John]

Could you adjust the on target position of the finder so that the target lies just inside the apex of the cross hairs rather than behind them, and note that position ?

Like this:

 

 

[Kon]

I have the Skywatcher RACI and it also has thick crosshair. It is fine when I am at f15 but f20 will be harder. (Stuart, I thought you were tracking, no?)

[Space Cowboy]

10 hours ago, John said:

Could you adjust the on target position of the finder so that the target lies just inside the apex of the cross hairs rather than behind them, and note that position ?

Like this:

 

 

Thanks John that's a good idea. 

[Space Cowboy]

10 hours ago, Kon said:

I have the Skywatcher RACI and it also has thick crosshair. It is fine when I am at f15 but f20 will be harder. (Stuart, I thought you were tracking, no?)

Thanks Kostas, I nearly asked you if you had a right angle finder. I'll have to persevere for now. Tracking isn't great if I can't polar align which was the case last evening in the bright sky.  

[Space Cowboy]

23 hours ago, michael8554 said:

If splitting a slightly defocused Venus on the crosshairs isn't accurate enough, you need a Flip Mirror.

Michael

I will look into the flip mirror option Michael though I've always been wary of how it might effect collimation with all the extra hardware hanging on my focuser. I did try a eyepiece wheel once but didn't trust it's build quality collimation wise.

Edited February 28, 2023 by Space Cowboy

[Kon]

4 hours ago, Space Cowboy said:

Thanks Kostas, I nearly asked you if you had a right angle finder. I'll have to persevere for now. Tracking isn't great if I can't polar align which was the case last evening in the bright sky.  

I found with my manual Dob that using the full sensor frame is fine with the thick crosshair but it is becoming harder when i get down to 640x480 ROI. The centre of the crosshair is not square to the sensor any more and I need to re-align it. I have tried what John suggested above to offset but when you go to the tight ROI, it is even harder. For visual the RACI is perfect.

[John]

4 hours ago, Kon said:

I found with my manual Dob that using the full sensor frame is fine with the thick crosshair but it is becoming harder when i get down to 640x480 ROI. The centre of the crosshair is not square to the sensor any more and I need to re-align it. I have tried what John suggested above to offset but when you go to the tight ROI, it is even harder. For visual the RACI is perfect.

Those are good points. I'm visual only so my solution is based on that. It's probably off-beam for imaging application.

 

[Space Cowboy]

5 hours ago, Kon said:

I found with my manual Dob that using the full sensor frame is fine with the thick crosshair but it is becoming harder when i get down to 640x480 ROI. The centre of the crosshair is not square to the sensor any more and I need to re-align it. I have tried what John suggested above to offset but when you go to the tight ROI, it is even harder. For visual the RACI is perfect.

How you manage to produce those images without tracking and with those thick crosshairs and also get such good focus especially on Venus I don't know 🙂  Have you tried the auto ROI centering on FC?

[Kon]

51 minutes ago, Space Cowboy said:

How you manage to produce those images without tracking and with those thick crosshairs and also get such good focus especially on Venus I don't know 🙂  Have you tried the auto ROI centering on FC?

Actually, I offset the target at the crosshair side as John pointed above and let it drift through the centre. It takes a few attempts and I usually rotate the camera to give me a long sensor drift from left to right.

I usually use asicapture but for my latest Venus was with FC and now I know what I am doing I will give it a try.

[Kon]

2 hours ago, John said:

Those are good points. I'm visual only so my solution is based on that. It's probably off-beam for imaging application.

 

Yes absolutely and I use that technique some times for my visual and most of the time for ISS imaging.

[Space Cowboy]

16 hours ago, Kon said:

Actually, I offset the target at the crosshair side as John pointed above and let it drift through the centre. It takes a few attempts and I usually rotate the camera to give me a long sensor drift from left to right.

I usually use asicapture but for my latest Venus was with FC and now I know what I am doing I will give it a try.

Apparently FC has an audible histogram and makes a noise which increases in volume as the planet appears on screen. 

[Carbon Brush]

Most scope fixings and mounts have a bit of flexibility or elasticity.
If your target hides behind the wires, gentle pressure somewhere on the mount will bring it back into view.
Release the pressure and the mount returns to the correct place.
When the target only shows while leaning on something, you are in the right place.
I have used this technique quite a few times on various combinations of scope and mount.

HTH, David.

[Space Cowboy]

SOLVED!

 

Sent the AE finder back and got this as replacement. Not tried on scope yet but crosshairs are nice and fine! Only 10 quid more and comes with a shoe! Looks far better quality.

 

https://www.firstlightoptics.com/finders/stellalyra-8x50-right-angled-correct-image-raci-finder-scope-with-bracket.html