Quark forward focus problem

[pragmatist]

So I’m using my Quark with an Altair 60mm ED doublet. My huge problem is I cannot achieve focus. At first I thought it was a backward focusing issue so I bought an extension tube but to my horror it’s a forward focusing problem and I haven’t a clue how to solve this. Any ideas would be appreciated. 

 

[Paz]

What kind of diagonal are you using, some have longer light paths than others and use up more of your in focus travel, leaving less spare travel inwards.

[Floater]

 +1 for above. 

I had the same problem and found that a 1.25” diagonal was essential. I could not focus using my 2” diagonal. All to do with the light path.

I eventually achieved focus using the 1.25” diagonal and a focal reducer. Can’t remember the specific configuration.

I have sold on my Quark but I recall  lots of difficulty and frustration to begin with. However, I recommend that you work on through with it - because the views are well worth the trouble. ?

[pragmatist]

9 hours ago, Paz said:

What kind of diagonal are you using, some have longer light paths than others and use up more of your in focus travel, leaving less spare travel inwards.

I’m using my 2” Altair dielectric so that could be the problem then.

[Paz]

3 hours ago, pragmatist said:

I’m using my 2” Altair dielectric so that could be the problem then.

It could be, a 1.25" will get your eyepiece further in. There's even quite a difference between types of diagonal. I've got a tak prism diagonal that focuses 21mm further back that my mirror diagonal (both are 1.25") and so is handy for me when running out of inward travel.

Even eyepieces vary, looking at my notes for example my 8mm Delos is in focus 6mm further out than my 10mm slv.

You might be able to measure how close to focus you are by sticking an eyepiece straight into the scope with no diagonal and seeing where it focuses for comparison.

 

[Davey-T]

Is that the 350f/l f/6 AA scope ?

According to Daystar the Quark should work with f/5 to f/9, I've used mine in an ST80, 400f/l f/5 OK with a 1.25 diagonal.

Some of these widefield refractors tend to be optimised for imaging so are a bit lacking in focuser travel.

As mentioned try it straight through to see exactly where you achieve focus without a diagonal.

Dave