135mm D-ERF to a 160mm D-ERF

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Ewan
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135mm D-ERF to a 160mm D-ERF

Post by Ewan » Wed Jun 28, 2017 9:20 pm

I am looking at upgrading my Baader 135mm D-ERF I use with my 152mm F5.9 scope.
I sent Baader a quick question & just got this reply back :-

'Dear Mr. Hobbs,

thank you for your inquiry.

I have to say that it is not very likely that you are losing much in this configuration. As the Quark has a VERY small etalon and also possibly a not so good telecentric compared to real optical telecentric systems wich are necessary for high end solar observing,

Therefore, if you enlarge the entrance light beam, you shorten the focal length of your system and therefore make it harder for the small SEMI telecentric in the Quark to work sufficient.

Also you get PLENTY of light with the 125mm. It may be even better to reduce the front end even further.

As we are only dealing with Solar Spectrum Ha Filters we dont know the optical design of the Quark. And we can not say it for sure.

Anyway, we sell our D-ERF Filer only without frame. The frame, we can only manufacture, if the customer buys the filter also from us.'

I have seen some stunning images on this forum & others at F ratios that should produce 'poor' results so should I just ignore the email reply I received as in the 'real world' things don't always happen as they should ?

I could always stop the ERF down a bit if I do lose contrast or detail.

Any advice on this would be much appreciated.
Atb

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krakatoa1883
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Re: 135mm D-ERF to a 160mm D-ERF

Post by krakatoa1883 » Fri Jun 30, 2017 7:52 am

Thanks for sharing. If the intended upgrade is from 135 to 152mm I don't see much difference in terms of resolution while you would certainly need to increase the EFL in order to match the F/D requirement for the etalon. But it is also true, as stated in Baader's reply, that this requirement allows some relaxations...

I know that someone uses the same 152mm scope as yours with an internal Baader D-ERF mounted inside the tube at some distance behind the objective, allowing the use of the whole aperture without actually installing a full-aperture front D-ERF. I have no personal experience of this but based on the images I have seen it seems to work fine.

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marktownley
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Re: 135mm D-ERF to a 160mm D-ERF

Post by marktownley » Fri Jun 30, 2017 12:26 pm

Hi Ewan,

Your 152mm/f5.9 will be running at a free aperture of 125mm with that 135mm DERF, which, gives a resultant f7.2 which is about right for the quark (ish!). Upgrading to a 160mm DERF, and running at 150mm clear aperture will give you a resultant f ratio of 6, which, with the quark will give you less contrast (wider bandpass), albeit with a slightly higher resolution. If you really want to use the full 6" aperture and get a 160mm DERF I would sell the 152/f5.9 and buy a 152/f8 frac instead, then you will get the resolution and the contrast. Personally I don't think you will see a huge jump in resolution from the 125mm aperture you have now compared to going up to 150mm.

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Re: 135mm D-ERF to a 160mm D-ERF

Post by Ewan » Tue Jul 04, 2017 9:39 pm

Sorry it's been a while guys & thanks for responding to my query.
Based on the response from Baader & yourselves I think I will just stick with the set up I have then, I wish sometimes re sellers would be a little more honest about a clients expectations.

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Re: 135mm D-ERF to a 160mm D-ERF

Post by Nicksolar » Sun Jul 16, 2017 1:29 pm

Hi Ewan, Since we became APM distributor I started playing around with APM gear. I've been imaging for some time with the Altair 152 F5.9 at full aperture and a Quark and I'm getting pretty good results so far as I'm sure you've seen especially on faint proms which look better at shorter F Ratios allowing short exposure duration.. However I prefer resolution over contrast, because I tend to process a certain way and I tend to use extremely fast exposure duration which I notice many do not. Having said that I recently took an APM 152 ED home from stock and I got a very nice image with it at F8 with the Quark. Then I tried an APM 1.5x Telecentric in front of the Quark, and although it was a bit "overcooked" on the APM, it performed OK. I think at F12 before the Quark you need pretty good seeing. Then I tried the Telecentric on the Starwave 152 F5.9 and it was really nice "sweet spot" I would say. It worked very well on the Starwave 152 F5.9 giving around F8.8 before the Quark resulting in F37 or thereabouts. It's quite a big unit, but very strong. Anyway I recently tried the prototype Altair 125mm F7.8 EDF with Quark and that I have to say was awesome. Very punchy. Not as much resolution, perhaps as it's 125mm aperture compared to 152, but on the other hand at about 4.1m focal length it worked very nicely with the 174 Sensor and illumination was quite even. I think based on my limited experiments so far, in your case, adding an APM 1.5x Telecentric and perhaps a full aperture ERF is definitely worth considering at least.

Nick

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Re: 135mm D-ERF to a 160mm D-ERF

Post by marktownley » Sun Jul 16, 2017 8:12 pm

To make it more cost effective you could use the APM telecentric like Nick says and mount the 135mm ERF you have internally sub aperture inside the OTA...
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