Battle of the Titans - the Peashooter vs the Light Thimble

[Stu]

Having about 30 minutes to spare, and knowing GRS was going to be fairly well placed at around 10.30, I popped my two smallest scopes on the Ercole for a bit of a shootout last night.

The 63mm Zeiss Telementor took on the 65mm TAL Alkor.

It wasn't a scientific comparison, none of mine are! I have been wanting to see how the Binoviewers worked in the Zeiss to help deal with floaters, whilst the Alkor can only take its own, special eyepieces so the floaters are there to be dealt with.

The Alkor's eyepiece alone gives x33. Add the Barlow and you get x83 and then add the spacer and you get x133. Pulling the eyepiece out of the Barlow a little way can also give you a boost in mag over and above these figures.

In the Zeiss I used the binoviewer with a variety of different GPCs giving me x57, x115 and around x186 I think.

Both scopes just have a gunsight type finder arrangement, which for Jupiter works surprisingly well. At x83 in the Alkor, Jupiter was small but pretty contrasty. Floaters were well controlled so I enjoyed the view which gave a decent amount of detail. GRS was clearly visible, with some reddish colour to it. The NEB was obviously darker than the SEB, and there was some polar darkening going on. Upping the power to x133 gave me better image scale of course, but colour and contrast reduced significantly and floaters got worse, becoming quite distracting. There was, however, more detail visible in the belts if I looked carefully. Not like I would see in a larger scope, but subtle variations along the edges which were quite clear. A quite amazingly sharp little scope which cost me little more than a used ortho!

At x57 in the Zeiss, the two main bands were clear and GRS was just detectable. It was as nice view but not that rewarding as the planet was too small. Upping to x115 gave me a view that was not dissimilar to the Alkor at x133 although the floaters were much better controlled and somehow the view was 'smoother' in that I felt a little of the fine detail was missing. GRS was probably a little more distinct, but some of the belt detail was harder to come by. I suspect this was more of an effect of the binoviewers than the scope, but further comparisons without the binoviewers will have to wait. Finding a way to get to around x90 would probably give best results. Upping to x186 with a 0.34mm exit pupil and even with the binoviewers my floaters became intrusive. The view was washed out but detail still there if you worked at it. CA was very well controlled in this scope, it wasn't something which caught my attention at all, I just didn't think about it which must mean it was barely noticeable; I hate CA!

My summary? For 63mm and 65mm respectively these two give amazingly sharp views for their size, and show useful detail on Jupiter. I'm sure a shadow transit would be visible in both  with last nights conditions. As I have found with other scopes, performance down to around 0.5mm exit pupil provides decent views, below this and it is floater city for me, and washed out detail.

The Alkor must present one of the cheapest ways of seeing reasonable detail on Jupiter including GRS and shadow transits, and no doubt Saturn when better positioned. With both scopes the optical quality shows through despite the small aperture. Alot of fun.

[happy-kat]

Interesting report, could you add these two scopes focal ratio please to the thread as I'm not familiar with either and don't know if peashooters or squat in length.

[Stu]

10 hours ago, happy-kat said:

Interesting report, could you add these two scopes focal ratio please to the thread as I'm not familiar with either and don't know if peashooters or squat in length.

Thanks very much. Of course.

The Zeiss is 63mm and 840mm focal length making it f13.3

The Alkor is 65mm and 500mm focal length making it f7.7. It has the tiniest secondary I've ever seen, not easy to collimate but I've managed to get it into a good position. The primary is fully collimateable but never needs touching once I adjusted it initially.

The Alkor is quite squat, the Zeiss more elegantly long and slim. I find the focuser on the Alkor too slack for my liking but have yet to find a suitable way of adjusting it. It's a tiny R&P, very good but just needs to be a little stiffer.

The Zeiss has a helical focuser plus an extendable drawer tube. This is a very flexible setup giving plenty of inwards focus and allowed me to reach focus with binoviewers and with various GPC combinations. The helical focuser is again a little too light for my liking but it stiffened up nicely towards the end of the range so I tend to set the drawer tube such that I operate in the stiffer part of the helical focuser's range which works well.

I meant to take a picture of the setup, will try to do it tonight.

[John]

Very interesting report on small but capable scopes Stu

I may give my 70mm TV Ranger a turn on Jupiter tonight, clouds allowing. It will be interesting to see how close it can get to the Tak FC100.

[Stu]

The slightly sad thing is that with young eyes I'm sure the results would be much better than I get with them.

I do find it fascinating though to see the results when viewing double stars as much as anything. Izar in particular shows a complete first diffraction ring with the secondary just there as a bulge in it of different colour. You've posted a good sketch of it before John. In the Tak the diffraction ring is barely there and the separation is far easier to see.

[Stu]

Some pictures here

[John]

Seeing is pretty decent just now - the 70mm Ranger is showing 4 belts and suggestions of a couple of festoons !

Don't know why I bother with all those other scopes !

[Kn4fty]

Thanks for the report Stu! What is the reason that one scope does better on your floaters that the other? Just curious because i deal with floaters, but haven't had them be an issue with my scopes. If its a design thing, then maybe I've been fortunate enough to avoid a scope that makes floaters noticable.

 

Rob

[Stu]

1 hour ago, Kn4fty said:

Thanks for the report Stu! What is the reason that one scope does better on your floaters that the other? Just curious because i deal with floaters, but haven't had them be an issue with my scopes. If its a design thing, then maybe I've been fortunate enough to avoid a scope that makes floaters noticable.

 

Rob

The only reason is that I was using binoviewers in the Zeiss and this helps reduce the visibility of floaters. Your brain combines the two images and because the floaters are only present in one eye (or at least in different places) it can process out the effects to a large degree.

Actually the best defense again floaters is aperture. They become visible below around 1mm exit pupil and for most people below 0.5mm is where they become tough to ignore. In round numbers, take 50mm, 100mm and 200mm aperture scopes and they will have 0.25mm, 0.5mm and 1mm exit pupils at x200 respectively, so aperture really helps in this regard. I don't see them at all at x200 in my 210mm Mewlon for example.

[Kn4fty]

Thanks Stu for the information. Guess it gives me a good excuse to  get a binoviewer. I never knew aperture would do that, but thinking about what you said, it makes perfect sense. 

 

Rob