Adc for visual- ZWO or Altair?

[markse68]

Hi there, not sure if this is the right section but it’s for something I want to look through so hopefully it’s ok here. I’m about to pull the trigger on a “cheap” adc for visual and wonder if anyone has an opinion whether to go Zwo or Altair? They look similar but the Altair is a bit cheaper. Zwo claims 1/10 lambda finish on 2deg prisms, Altair doesn’t mention quality but their prisms are 2.5deg. Is there generally a quality difference between the 2 companies products? The Zwo cameras seem to get more mention than Altair but that’s likely more to do with image sensor etc- but engineering-wise, fit and finish? I doubt there’s anyone who has both their ADCs to compare so it’ll be very subjective I guess. The prism difference would mean the Altair could compensate for more atmospheric dispersion but would that be necessary for me looking at the planets from now on?

thanks,

Mark

Edited June 12, 2020 by markse68

[CraigT82]

I can't comment on zwo vs Altair as never had my hands on the altar version (I think its the same as the omegon branded one?) but just to note that you can get more correction on any adc by increasing distance between prisms and eyepiece. A T2 extension between adc body and ep holder would be ideal but even just pulling ep out of holder a bit would give you a bit more correction if needed. 

On my fullerscope I had to move the mirror up the tube a bit to be able to focus with the adc in place. 

 

[markse68]

21 minutes ago, CraigT82 said:

I can't comment on zwo vs Altair as never had my hands on the altar version (I think its the same as the omegon branded one?) but just to note that you can get more correction on any adc by increasing distance between prisms and eyepiece. A T2 extension between adc body and ep holder would be ideal but even just pulling ep out of holder a bit would give you a bit more correction if needed. 

On my fullerscope I had to move the mirror up the tube a bit to be able to focus with the adc in place. 

 

Thanks Craig- I saw you had the Zwo one. Did you have to shift the primary even with a Barlow?

[CraigT82]

25 minutes ago, markse68 said:

Thanks Craig- I saw you had the Zwo one. Did you have to shift the primary even with a Barlow?

Yeah even with Barlow! At the time I had quite a tall focuser but now have a moonlite which has a much lower profile and I returned the mirror to its original position after fitting that. 

[markse68]

On 12/06/2020 at 13:22, CraigT82 said:

Yeah even with Barlow! At the time I had quite a tall focuser but now have a moonlite which has a much lower profile and I returned the mirror to its original position after fitting that. 

Hmmm, I’ve only got about 20mm inward focuser travel from focal plane so maybe 30 for some eps and I don’t really want to shift my primary- the secondary is on the small size already, so I don’t think either of these are going to work. 🤔 I’ve found and ordered some cheap prisms on eBay and have a cunning plan evolving....😉

[markse68]

Btw, anyone any idea how much a 2x Barlow shifts the focal point or is that a complex thing to determine?

[John]

53 minutes ago, markse68 said:

Btw, anyone any idea how much a 2x Barlow shifts the focal point or is that a complex thing to determine?

Depends on the focal length of the barlow I think. Not a spec that is regularly published

 

[markse68]

2 hours ago, John said:

Depends on the focal length of the barlow I think. Not a spec that is regularly published

 

After I wrote that I noticed Jupiter and Saturn in a clear sky so took the scope out to measure it- and oh boy am I glad I did as they were superb this morning! Best I’ve seen ever! So sharp and contrasty and the GRS obliged too! Clear banding on Saturn- so sharp and 3D. Mars wasn’t too shabby either- definitely some darker markings on the disk. Strangely elongated though- I wondered if it was atmospheric distortion but actually I wonder could it have been the polar caps just reflecting a lot more light causing the distortion? Definitely bright areas at the N and S poles- must be. Hopefully a taste of good things to come- so excited as the planets are already besting what I saw all last year

Back to the barlow thing though it’s a bit confusing. My Tal 2x didn’t change the focus just shifted the ep out 30mm- the length of its body. An AE 2x I also have shifted the focuser IN by about 7.5mm and the ep out the length of its body- 43mm. It’s too late (early) and my brains foggy so I’ll have to think what this means tomorrow 🤔

Edited June 14, 2020 by markse68

[Paz]

I can't compare the two makes but I've got a ZWO and it does what it says on the tin. It does take up some light path and there is a bit of workload involved in setting it up, so I don't use it on short sessions or if I'm using anything else that needs the available light path, like say a filter wheel.

[GTom]

Any update on these two?

My planned imaging train: lx200 10", Powermate 2x, ADC, Filter wheel, Altair 174m camera.

[Don Pensack]

On 13/06/2020 at 17:22, markse68 said:

Btw, anyone any idea how much a 2x Barlow shifts the focal point or is that a complex thing to determine?

All Barlows will move the focal plane of the telescope outward.

IF it moves the focal plane outward by exactly the length of the Barlow's barrel above the lens, it will be parfocal with the eyepiece when the eyepiece is used without the Barlow.

IF it moves the focal plane outward less than that distance, it will require in-travel of the focuser.

IF it moves the focal plane outward more than that distance, it will require out-travel of the focuser.

I have run into Barlows that do all 3.  More have required in-focus than out-focus.

How much in-travel or out-travel is required will depend on the spacing between the Barlow and the eyepiece, too.

 

So it will vary from Barlow to Barlow as to whether you need additional in-focus or out-focus.

[Louis D]

For the out-travel case, I generally just don't insert the Barlow all the into the focuser.  I just insert it until the eyepiece pops back into focus and tighten it down.