Looking for Advice - Barlow or Powermate

[evltoy]

Hey All,

I hope everyone is well :)

I'm currently looking at getting either a TV 2x powermate or a 2x Explore Scientific 2" Barlow.

This would be mainly used for imaging planets with my 8" SCT, zwo ADC and ASI462 camera, but I cant see why I couldnt also use it on my ED80 with a APS-C or Full frame DSLR.

Other than I having to get a 2" visual back for the SCT, can anyone see any issues I could came across with either of the above setups?

Also out of the 2, which one would be more suited for my setups?

Cheers
Wayne

[Merlin66]

using the x2 barlow/ PM would give you f20 on the SCT which is good for planetary imaging (Target x5 the pixel size for f ratio)


The x2 PM is only available in 2" fitting.
Why go for 2" when for planetary imaging, the 1.25" would work?
A x2.5 PM (in 1.25") would be OK and you can use the TV T thread adaptor to give a solid, minimum distance to your camera.
(I use the x2.5 regularly for solar imaging with the ED80 and the ASI 1600)

[evltoy]

Thanks ken for the information.

The reason why I was looking at the 2" was to be able to use it with my DSLR (full frame) on my ED80. I'm trying to kill 2 birds with one stone.

I will one day make the move to the ASi1600 or ASI071MC

When imaging, would I notice any differences between the TV PM and ES barlow?

[Merlin66]

OK
The ES "Barlow" I have is actually a telecentric (the magnification doesn't vary (much) with increasing back focus) similar to the Powermates.
The only real difference for me is the lack of a T thread adaptor for the ES version. This leads to sloppy fitment and sag with larger cameras.
Just my 2c

[evltoy]

Perfect! The slop in connection for heavy cameras is good to know. I'm running M48 connections with my DSLR so I'm hoping this will not be too much of an issue.

On another note. I do have a 2" Saxon barlow, but I cant get focus with it on my ED80 and DSLR. I have tried all different ways to connect it and can only get focus with eye pieces.... very frustrating to say the least.

https://www.opticscentral.com.au/saxon-2x-ed-barlow-lens-2-with-1-25-adapter.html

[Merlin66]

Wayne,
No sure how you connect M48 threads to barlows/ powermates. You'd need some special adaptors??


The positioning of the barlow and the backfocus is sometimes an issue.
I haven't found any issues with my ED80 but then again I have 50 years of various adaptors/ spacers/ doohicky dingbats etc.

[astro744]

If you go Powermate you’ll also want the T-ring adapters when imaging. These replace the visual top half of the Powermate to ensure correct spacing.

See https://www.televue.com/engine/TV3b_page.asp?id=53&Tab=_acc

Note there are different models for different Powermates.

Note also the 2.5x as pictured on the Tele Vue web site has the longer full diameter barrel presumably threaded for 1.25” filters (never seen a picture of the new one from below). The older and original Powermate as pictured on the Bintel web site (and many foreign vendors) has a stepped barrel and is not threaded for 1.25” filters. (I can confirm this as I have one).

[Merlin66]

Astro,
The T thread adaptor is for rigid connection to the camera. It also reduces the backfocus overhang. There's no "correct spacing"
I've had a few PM's over the years and still use the x2.5.
My x2.5 is a smooth barrel with a filter thread. I've never seen the stepped barrel.

[evltoy]

hehe, Mu current barlow can be pulled apart and M48 extention tubes etc can be connected together.

[evltoy]

the TV is sounding more like the right way to go.... but at a big cost

[astro744]

Ok. Thanks. Maybe I could have worded that better. I was referring to the graph on Tele Vue web site and the first para directly under the graph talking about 0mm position.

See https://www.televue.com/engine/TV3b_page.asp?id=53&Tab=_app

See here for image of original Powermate: https://www.bintel.com.au/product/tele-vue-powermate-2-5x/?v=322b26af01d5

Sometimes when sold used the bottom cap is on in the photo so you don’t know which one you are getting. Both work well, just the newer (at least within 10 maybe 15 years) takes filters.

[Merlin66]

OK, I see what you're looking at....
For the purposes of the comparison graph, the "zero" position shown is based on:
(Imaging through a DSLR with the Powermate™ T-Ring Adapter and camera T-Ring — without added extensions — brings the focus position to 0mm.)



which would bring the focal plane (the camera chip) to 55mm above the T-ring adaptor.
If you use the T-ring adaptor and connect directly to the camera (ie ASI 174 etc) the chip would lie 17mm above the T-ring adaptor.


This would be at minus 38mm on their graph......
I think the data is missing ;)

[astro744]

Thanks for the explanation. I just took some measurements:

Height of 2” Powermate with 2”-1.25” adaptor removed = 119mm (with bottom cap on).

Height of 2” Powermate with upper visual piece removed and replaced with a T-RING FOR TELE VUE 2X POWERMATE (printed on side) = 73mm (with bottom cap on).

Difference is 43mm. With the Tele Vue T-ring option you simply attach the T-Mount adaptor for your DSLR to the T-ring.

If not using the Tele Vue T-ring adaptor you connect the camera body T-mount adaptor to a 2”-T2 adaptor and slip this into the 2” visual part of the Powermate. The DSLR ‘film’ plane is then 43mm further back (plus thickness of 2”-T2 adaptor, these days quite thins at approx 3mm), than if using the Tele Vue T-ring.

I’m not quite sure I fully understand the Tele Vue graph. They label it FOCUS POSITION FROM TOP SURFACE, but is that from top visual surface or top t-ring surface?

Anyway I’m not an imager and just dabble in the occasional lunar eclipse photo through my ED80 or TV-101. I too have all the Tele Vue adaptors and Powermates mainly for visual. A 35mm Panoptic with 4x Powermate makes an outstanding (but very heavy) 8.75mm eyepiece with huge eye lens and plenty but not too much eye relief.

To the OP. Powermates do come up for sale in the classifieds but sell usually reasonably quickly (depending on asking price of course).

[Startrek]

I’ve used my full compliment of TV Powermates for both planetary imaging and visual observing. I have Barlow’s as well but rarely use them in favour of PM’s
The TV T ring adapters fit most Astro cameras ( ZWO ) direct and DSLR’s with a T ring
For planetary when using the 4 x Powermate and 5 x Powermate I have to use a 35mm extension adapter to achieve focus , the combo stack with camera hanging out of the focuser in my Newt is still fairly rigid, no issues
For visual, Powermates are excellent for both DSO and planetary observing ( 12” Goto dob )I also have a large collection of TV eye pieces including Delos , Panoptic, Ethos and Apollo 11
Once you’ve used TV PM’s for a number of years for both forms of Astronomy you be hesitant to go back to a Barlow

Cheers

[evltoy]

I thank you all for sharing your knowledge and experiences on the topic.

I'm going to give the SE 2x Barlow a shot first and see if I can get focus with my setups.

If I stay in the hobby long enough I will invest in the TV PM in the future. Due to cost and from what I have read on other sites, the extra cost of a TV PM over a ES barlow does not justify the performance difference... well I dont believe I will notice the difference being so new to the game.

Thank again all
Keep safe
Wayne

[Spacer]

2.5x powermate any day over 2x barlow.