55 42 35 13 2inch - which Barlow & diagonal best?

[25585]

Now having 4 2 inch eps to use on my C8 and Genesis, which diagonal and Barlow would be the best combination?

I have the TV diagonal that came with my Genesis which is 2 inch, but want another for the C8 which I bought as OTA only. 

[John]

My diagonals:

Tele Vue Everbright (x2)

Astro Physics Maxbright

Baader T2 Zeiss (which can be adapted for either 2" or 1.25" but will slightly vignette the widest 2" eyepieces)

The AP is probably the best pure 2" diagonal that I've used but the Everbrights are pretty good as well. Lots of other less costly choices around though. The Baader Zeiss is used in my Tak F/9 100mm flourite pretty much exclusively. They might no be so good in a fast frac like the Genesis.

I currently have a Baader Vip Barlow which is optically excellent but I use it pretty much exclusively with the Leica ASPH zoom. Other very nice 2" barlows / extenders that I've owned are the TV Powermate, the ES 2" 2x Focal Extender and the Antares 2" 1.6x barlow which was a really nice Japanese optic for it's price but the latest versions need a lot of inwards forcuser travel.

Are you looking for an SCT fitting diagonal for the C8 or will you go SCT-2" adapter and then push fit diagonal ?

 

[Louis D]

Bill Paolini did a shootout of various mirror and prism diagonals a few years back that might be worth a read for you.

Stick with a telecentric magnifier design like the TV Powermate or ES Focal Extender with long focal length 2" eyepieces or you'll get "edge of field cutoff" as I call it, not just vignetting.  It literally looks like a new field stop has been introduced inward of the actual field stop when a widest field eyepiece is inserted into a normal 2" barlow.  That, and the exit pupil gets messed with which can be difficult to deal with.  With a telecentric design, the eyepiece continues to function as it always did without one in the focuser, just at a higher power now.  They also don't require a lot of refocusing, either, like a regular barlow.

[25585]

I was considering a Powermate 2x have to save a bit more as costlier than an ordinary Barlow. 

As far as diagonals , my C8 is the scope I use least but want to use more now I have a Skytee-2 mount. 

I was not aware there were specific SCT diagonals! I guess I would prefer a diagonal that could be used on my Genesis F5 as well as C8 F10. So presumably a SCT 2 inch adapter & push fit diagonal allowing the older diagonal to be used on my C8 (one of the orange tube Celestron ones). 

[Merlin66]

In my experience, you won't use a Barlow for visual in a SCT. Change the eyepiece....

I use my Genesis diagonal occasionally in the C11 with the SCT to 2" fitting, but I find the Meade 2" SCT diagonal to be the most used.

 

[Louis D]

4 minutes ago, Merlin66 said:

In my experience, you won't use a Barlow for visual in a SCT. Change the eyepiece....

I use my Genesis diagonal occasionally in the C11 with the SCT to 2" fitting, but I find the Meade 2" SCT diagonal to be the most used.

 

I have to agree.  If you're already at 2000mm focal length, why do you need to barlow at all?  For the cost of a 2" 2x Powermate (£302.00), you can get several very nice shorter focal length eyepieces and put a lot less stress on the diagonal than having a large, long focal length 2" eyepiece sticking out of a fairly long Powermate.  The Powermate also weighs 22 ounces, about the same as a 22mm Nagler T4.  That's nearly 3 pounds all together.  You already have a nice range of eyepieces according to your signature.  You might want something in the 7mm to 9mm range for highest power on the SCT; but otherwise, you're pretty well set.