Some Hi-res Ha making the best of a quiet period

[longtech]

After April's bonanza of activity the past week has been comparatively slow...however on May-01 I just had to shoot something and managed to find some interesting captures in the quick afternoon session.

Lunt LS152THa SS with 4x Powermate and Baader 160mm D-ERF...RCX-Pro render to TIFF, 400/1000 frames AS2!, deconvolution, PSCC

All images clickable for full res...wide shots are 4K (4096x2160)...tight shots are cropped from the 4K

Thx for looking!

[Ewan]

Nice set there Longtech, at least you caught something which is more than me over the last few weeks.

[Valery]

I like this image the most:
A031-C100-4K-050116-AST603-PS06001-NR-HDR-CR1.jpg

I think you have some problems with etalon tuning and may be with it's
not 100% squire to the optical axis or your blocking filter + camera and
Povermate being not square.
On the image I noted as the best to my taste all is OK and uniformly
illuminated.


Valery.

[Derek Klepp]

Still some ARS there though just not on a grand scale

[yltansg]

Like the 5th image best

Alfred

[Montana]

I like picture 2 best, smooth as silk

Alexandra

[michael.h.f.wilkinson]

The fifth is my favourite

[eroel]

Very very good images, though they show a bit of uneven illumination. Could be what Valery says, or the 4X Powermate.
I have the same problem of uneven illumination with my 4X Powermate on a 6" f/12 AP refractor using a Baader Herschel wedge.
Best regards,
Eric.

[Bob Yoesle]

Powermates are not true telecentrics. You might be interested in Christian Valadrich's excellent analysis:

In order to benefit from the full performance of mica-spaced F-P etalons, the following requirements are to be met:
a) Use of a true telecentric lens system (such as Baader TZ or Beloptik). So called "telecentric Barlow lenses" are not telecentric and will give results of lower quality. The good news is that true telecentric lens systems give good performance, even when used at a focal length different to their designed focal length (within some limits ...)
b) Check out the the squareness of the F-P etalons to the optical axis. In other words, there should be no compromise on the mechanical set-up. As a rule of thumb the maximum allowance for the tilt is 0.1°.
It is a very easy to check out the squareness of the F-P etalon by auto-collimation :
- Place yourself at a few meters from the objective of your refractor.
- You should see : the cercle of the objective, the cercle of the etalon, and ... the reflection of your eye on the etalon.
- The reflection of your eye should be centered on the image of the etalon and on the objective.
Otherwise you should arrange the mechanical set-up.
c) The longer the focal ratio the better the performances are. F/D 30 seems to be a good starting point.

See: http://www.astrosurf.com/viladrich/astr ... lar/FP.htm

[longtech]

Thank you all for the kind words and suggestions.

Valery and Eric,
I do indeed have an issue keeping the sensor square to optical axis mainly due to the weight of the camera which is almost 6lbs. The effect is compounded by the sensor size which is nearly 31MM x 16MM.

The etalon however seems to be very closely aligned to the objective... I'm using it in the stock LS152 F6 configuration...the Powermate is placed after the B3400 blocking assembly...whenever I place the smaller ASI174 behind the Powermate the illumination and tuning are both even but when I swap in the big camera I really need to struggle with the alignment between the focuser and camera...I've designed an accessory the supports the camera's weight and allows adjustment in the X & Y axis while allowing the focuser to control the Z-axis (along optical axis) position...the parts are machined but I just haven't had the time to assemble and test.

Bob,
Thanks for the tips and the link...I have a TZ4 I purchased for a separate project but I had not considered using it on the LS152 since I use it in the stock config where the etalon assembly is designed for the F6 light cone of the OTA.
...so my question to you; is my assumption correct that the TZ4 would not make a significant difference in the case where its used behind the etralon rather than in front?

Thx again to all :-)

[marktownley]

Nice pics!

You better post some pics of your new gadget when you assemble it, we do like a nice bit of engineering

[Bob Yoesle]

Bob. Thanks for the tips and the link...I have a TZ4 I purchased for a separate project but I had not considered using it on the LS152 since I use it in the stock config where the etalon assembly is designed for the F6 light cone of the OTA.
...so my question to you; is my assumption correct that the TZ4 would not make a significant difference in the case where its used behind the etralon rather than in front?

Ooops, you're right, I blew it by thinking you were using the TZ4 for a focal plane filter. In the LS 152 collimator based system the downstream amplifier itself shouldn't make that much difference -- but you could try it to see.

the Powermate is placed after the B3400 blocking assembly

I have found alignment issues to be of very high importance in most cases no matter what the etalon position, as the sensitivity to going off-axis does affect contrast performance, even with my front mounted etalons and no additional amplification. Making sure focusers, cameras, etc. are square and on the optical axis therefore does seem to make a noticeable difference.

[longtech]

Don't worry Mark...I have a couple of goodies to show the group shortly ;-)

Bob, when I get a few free days to dig in to my planned mod project, your post and link will be very helpful..thx again