How common is pinched optics in the winter on Esprit APOs?

[Deadlake]

18 hours ago, Adam J said:

Ok it took me only 5mins on astrobin looking for images with bright stars in them to find a pinched TSA-120. 

https://www.astrobin.com/271304/C/?page=3&nc=user

I did not even get a significant way through the TSA-120 images to find it. Perhapse it was taken at -30c but I really doubt that. 

Just goes to prove that if you go looking for problems on the internet you will always find them. 

 

How do we know what the temperatures where when the photos where taken? I'm trying to work out how you are correlating the image shown to low temperature.

For example why not collimation is an issue? I know what dealer who collimated all the scopes he gets in that have been through QC and that applies from Far East to premium manufactures. 

[Adam J]

9 hours ago, AndyThilo said:

It's certainly a risk with any refractor, especially imaging in low temperatures. I just think the manufacturing of the Esprit 80's and to less degree the 100's has gone downhill. Certainly there seemed to be little in the way of inspection or QC. I get a little with my 130 triplet, but only on really bright stars at lower temperatures and certainly not enough for me to worry about.

https://www.astrobin.com/full/srei8d/0/

Nice image. Yes I think that the 80s have always been a little more hit and miss than the others, that I will agree.

[CraigT82]

5 hours ago, Deadlake said:

How do we know what the temperatures where when the photos where taken? I'm trying to work out how you are correlating the image shown to low temperature.

For example why not collimation is an issue? I know what dealer who collimated all the scopes he gets in that have been through QC and that applies from Far East to premium manufactures. 

Quite helpfully, Astrobin allows user input of the ambient temp at capture... 

 

[Adam J]

5 hours ago, Deadlake said:

How do we know what the temperatures where when the photos where taken? I'm trying to work out how you are correlating the image shown to low temperature.

For example why not collimation is an issue? I know what dealer who collimated all the scopes he gets in that have been through QC and that applies from Far East to premium manufactures. 

We know that they chap with the profile that says he lives in Texas and who took the image in early autumn was not imaging at any seriously negative temperatures, more likely positive and by a large margin. 

Edit: as noted sometime people even note the temperature down on astrobin. +10c in that case. We can assume Celsius given the bloke is french. 

My point is not that they where taken at low temps it's that these Takahashi scopes are pinched and form locations and dates we can rule out very low temperature in a number of cases. If it's happening to Takahashi and Borg and WO it's not just an esprit problem, it's a problem that's more common across the board than some people want to admit. OP could have asked about almost any scope and any brand and someone would have come back with a sob story about their pinched scope. 

Edited April 28, 2021 by Adam J

[Louis D]

20 hours ago, CraigT82 said:

Quite helpfully, Astrobin allows user input of the ambient temp at capture... 

 

Is that in C or F?  For US submittals, does it autoconvert from F to C?

[CraigT82]

18 minutes ago, Louis D said:

Is that in C or F?  For US submittals, does it autoconvert from F to C?

The input box asks for ambient temperature in centigrade. US users would have to do their own maths! 

[Louis D]

55 minutes ago, CraigT82 said:

The input box asks for ambient temperature in centigrade. US users would have to do their own maths! 

Or blow it off and mess up everything because they can't be bothered. 😉 😁

[astrojohnarthur]

Sorry to come late to the party but I’ve just bought an Esprit 120. The first night I used it, I didn’t notice a problem with pinched optics but on the second night, when it was -2 outside, it was very obvious with hexagonal defocused stars during focusing routine. Looking back at my previous images, the problem was just visible there too. 
 

Fortunately, I’ve experience of pinched optics from my Altair Astro 480mm f6 triplet which gave “iron cross” stars from the 4 screws holding the lens elements. Backing off each of the 4 screws by 1/8 turn fixed the problem completely. 
 

This morning, I’ve accessed the 6 (x3) hex screws holding the Esprit 120 lens elements by unscrewing the dew shield and then removing the sticky backed black felt strip overlying the screws. I’ve backed all 18 off by 1/8 turn and then put everything back in place. I live in very cloudy Northern Ireland so it will be a while before I can see if this has worked but I’m hopeful. 
 

The image is from my 480mm f6 triplet prior to backing off the 4 screws -“Iron cross” stars.

Edited March 17, 2023 by astrojohnarthur

[Lumos]

Well you made me go back and check my images from my Esprit 150 that I took last month when it was below freezing but to my eye they  look OK. When you loosen the screws is there a risk that they will be too loose in summer?

[astrojohnarthur]

Judging by my experience with the 480mm, no. It’s only 1/8 of a turn. The 480 has been great ever since - still In use at about 8 years old now. My trouble is I live near the western coast of N Ireland and it could be quite a while before I get out again to check the Esprit 120. 
 

I’ve included “before” and “after” pics with the 480mm. Different cameras and total integration times but same target. Iron cross stars on the before.