Effects of pinched optics

[Peter Shah]

I recently was in the market for a small portable set up, something I was able to throw in a small case and take with me on holiday. I decided to go for the TS APO 65Q, little Quad Apo refactor.

The first night it arrived believe it or not was clear, Orion was in a reasonable position to try it out. I wanted to see how wee it performed on a full frame sensor, I wasn't expecting much from it So I just threw on my Sony A7s focused it in and did a single 20s unguided shot of M42. My first impression was it looked okay with a slight bit of astigmatism as i brought it into and past focus. When I took a closer look i had little triangular stars where there should have been round. A classic sign of pinched optics...... Pinched optics are really nothing to worry about and something that is quite common and very easy to put right.  After three mins of tweaking the result was nice round stars with no sign of astigmatism. To be honest it really corrects quite well across a full frame sensor across a large format sensor especially for such a for such a cheap small scope. 

 

 

 

 

 

 

Edited July 1, 2018 by Peter Shah

[Tweedledee]

Very nice. Glad you got it sorted so quickly. ?

 

That NGC1981 is a lovely bright cluster which gets overlooked because of its nebulous neighbour.

 

You got the Running Man as well. ?

Edited July 1, 2018 by Tweedledee

[+Ibbo]

Good result Pete.

 

My 132 suffered with pinched optics among other things.

 

It took a hammer and chisel to free the objective I kid you not.

It was second hand and really showed up in cooler conditions, I can only believe that the previous owner had been in and cleaned and nipped the triplet up nice and snug ?

 

 

[Peter Shah]

14 hours ago, Ibbo said:

Good result Pete.

 

My 132 suffered with pinched optics among other things.

 

It took a hammer and chisel to free the objective I kid you not.

It was second hand and really showed up in cooler conditions, I can only believe that the previous owner had been in and cleaned and nipped the triplet up nice and snug ?

 

 

Normally shows up when its colder. I'm sure they are setup perfectly in the factory where  climate is much warmer. 

[BAZ]

A good post there Pete.

The same thing can happen to reflectors as well when the mirror clips are too tight. It happened to my 300P when I first cleaned the mirror, I pooped my pant's I thought I had killed it. Again just a tweak was all it took. Apparently the mirror has to "float", that is be retained but not gripped by the clips. 

[philjay]

Surprisingly common this, I had a OO Usa 102ed doublet some years ago which did this when temperatures dropped below 0. A slight loosening of the retaining ring sorted it. Wish I still had that scope.

[Peter Shah]

3 hours ago, BAZ said:

A good post there Pete.

The same thing can happen to reflectors as well when the mirror clips are too tight. It happened to my 300P when I first cleaned the mirror, I pooped my pant's I thought I had killed it. Again just a tweak was all it took. Apparently the mirror has to "float", that is be retained but not gripped by the clips. 

You are correct the mirror does need to float but if your optics are fast then there is less tolerance as any slight movement will show up especially with some of the hi performing correctors you can get real ugly stars. I have a method for setting up my AG12, at F3.8 its very challenging to set up correctly so that its stable through all seasons but that  goes for all fast Newts though......