5x Powermate with SW MN190 Mak-Newt Telescope

[Gina]

I'm thinking of trying planetary imaging and buying a 5x Powermate to use with my Skywatcher MN190 Mak-Newt scope.  This would convert a 1000mm FL scope into one of 5m FL (or a bit more) at f26.  I already have a ZWO ASI120MC-S camera and wondered if this would be considered a sensible setup.

Edited July 2, 2019 by Gina

[JamesF]

I think 5x might be a bit overkill, but there doesn't seem to be much that sits nicely between 3x and 5x.  I wasn't hugely impressed with the only 4x barlow I've tried.  The problem when you extend the focal length that much is finding the target, because you have such a small area of the sky on the sensor.

Do you already have anything smaller that you could use to step up the magnification a bit at a time whilst making sure the target is still centred?

James

[Gina]

I have 2x and 3x Barlows.

[Gina]

This is a comparison of 3x an 5x with ASI 120MC-S and Jupiter.  I thought the 3x Barlow gave a rather small image but alright as a finder, of course.  So would 2x.

[Gina]

I was able to find Jupiter last night with Baader Hyperion Zoom eyepiece and 3x Barlow by starting at 24mm and then going down to 8mm.  Unfortunately, Jupiter was still just a little dot.

[Gina]

I guess I could try the 3x Barlow before spending nearly £200 on the Powermate.

[MarsG76]

The 5X PM is powerful.. I have it and hardly every use it for my imaging.... the sky has to be absolutely perfect for it to be useful.... f26 might be ok for a 190mm aperture, but f50 on a 8" SCT it's too much.

 

[JamesF]

I would do that I think.  If you want a bit more than 3x then you could perhaps make up a spacer to go between the barlow and camera.

Overall image size on the sensor isn't really that important for planetary imaging.  What you want to do is to try to make sure you've captured all the detail available at the limit of resolution of the OTA.  A rough guide for achieving that is to have the focal ratio at five to six times the pixel size of the camera (measured in um), which is why some people were imaging at upwards of f/30 when the SPC900 was popular.  Beyond that you get a bigger image, but no more detail, and it's harder to do, so you might as well make the image bigger in processing and save the bother.

James

[Craney]

There is a 4x powermate available.

[Gina]

Yes but only in 2" version at £100 more.

[JamesF]

Which is why I've not tried it

James

[Gina]

There is an enormous difference in price between Barlows and Powermates.  Is this really warranted?

[Nigella Bryant]

I use a 5x powermate on my f4 Newtonian but Jupiter and Saturn are to low to use such power. It gives me f20 but absolutely terrible through the thick atmosphere. I'm only going to try my 3x Barlow next time I'm able to image. Sadly not tonight, going away tomorrow. When Jupiter is higher in a few year's I'll be using the 5x powermate. Meantime no.

[JamesF]

Powermates are more complex optically because they're pretty much telecentric (the 5x one may be not quite as good as the others in that respect, from memory).  That may be a plus in some cases, but it does mean you can't add extensions between the Powermate and camera to increase the magnification as you can with a barlow.  I assume the greater complexity accounts for some of the price differential.

James

[John]

58 minutes ago, Gina said:

There is an enormous difference in price between Barlows and Powermates.  Is this really warranted?

The Powermates are practically invisible when in the optical train, the only impact you see is the amplified image. They are quite complex optically with 4 elements one of which has steep curves which need to be ground and polished with great accuracy. I also believe that they employ low dispersion glass elements withn the design.

There are though a couple of alternatives to the Powermates which have simililarly enhanced performance but at less cost - The Explore Scientific Focal Extenders and Meade TeleXtenders.

 

 

[Aussie Dave]

There's the 2.5x PowerMate 1.25" Gina which I had for quite a while. There wasn't much difference I found from the PowerMate to my 2x Barlows which I have quite a few of including a couple of ED Barlows although conditions here aren't often great, plus I think the planets are very low in the sky for you there and will be for some years. You won't see a vast improvement, it will be minimal at best. I ended up selling my 2.5x PowerMate recently as it wasn't getting used. I'll just stick to my better quality Barlows for when seeing conditions are good or better while the planets are high in the sky here in Australia or not bother with them at all. I can not justify the new prices of them. If you were to buy one try and pick up a nice used one, at least then if you're not happy with it you can re-sell it and get your money back.

Edited July 3, 2019 by Aussie Dave

[Gina]

Thank you everyone.  That has clarified things very well.

Edited July 3, 2019 by Gina
typo

[Tommohawk]

Just another thought - the 5x powermate is very sensitive to the working distance in terms of the actual magnification - see here. The actual mag is likely to be rather lower with an ASI120MC and no EFW because the working distance will be quite close, especially if you remove the EP holder section and connect with the dedicated connector. If you leave the EP holder in place and connect using a 1.25" nosepiece the distance will be correspondingly greater. 

That said, as Nigella commented, even connecting directly gives too much mag for current conditions for sure - I tried last night and the results are very poor. (Quatto 10 with  5x, so same F20)

BTW if you use Firecapture you can get an estimate of the actual mag from the imaging log - it shows the system EFL. 

The TV powermate does seem an exceptional piece of kit, and I've had excellent results in previous years - just depends how patient you are. 2022 looks really good!