Sell the Aries DERF or not to sell?

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Sell the Aries DERF or not to sell?

Post by Starry Jack »

I've been experimenting with and without my prized Aries DERF on my 6" achro and Quark. In my last test at full 6", the Aries gave me better images live (video) and stacked (better grayscale ranges, details...). The images without the Aries were still amazing, but with the Aries, no question better.

The Quark is said to handle 4" to 5" very well and maaaaaaaaaybe up to 6" without any DERF at all. I'm wondering if the Quark was overloaded with light so the Aries added value because of that.

I'm going to try and mask down today to 4"-5", but I'm having difficulty making the masks.

Ultimately I'm selling most of my equipment so I can buy a 4"-5" APO and I'm trying to determine if this piece of equipment can be replaced with an internal DERF like Marty does (and WHO can argue with Martin's results): https://www.baader-planetarium.com/en/b ... ed%29.html.

Attached is the wavelength chart of my Aries for comparison to a Quark.
Aries DERF.jpg
Aries DERF.jpg (128.23 KiB) Viewed 510 times
Thanks,
Jack


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Re: Sell the Aries DERF or not to sell?

Post by DeepSolar64 »

According to DayStar a Quark equipped scope is supposed to be fitted with an ERF if over 80mm in aperture.


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Re: Sell the Aries DERF or not to sell?

Post by Starry Jack »

According to DayStar a Quark equipped scope is supposed to be fitted with an ERF if over 80mm in aperture.
Yikes! My memory must be failing...I'd forgotten that.

OK...Hmmm...but could it be successfully replaced with the Internal DERF by screwing the Baader or equivalent to the nose of the focuser?

Much cheaper...

Jack


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Re: Sell the Aries DERF or not to sell?

Post by DeepSolar64 »

You gotta be safe, you don't wanna damage your Quark and especially your eyes!!


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Re: Sell the Aries DERF or not to sell?

Post by Starry Jack »

True that!


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Re: Sell the Aries DERF or not to sell?

Post by marktownley »

Keep the Aries ERF Jack.

I've had to replace the blocker on my Quark after about 5-6 years...


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Re: Sell the Aries DERF or not to sell?

Post by Starry Jack »

When Mark speaks...I'm gonna listen! Much appreciated for the insight. I'll keep it.


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Re: Sell the Aries DERF or not to sell?

Post by RodAstro »

Hi Jack
Firstly Daystar recommends a ERF over 80mm but this can be a UV/IR filter up to 150mm according to their latest recommendations.

Secondly the Baader DERF has the same coating as the Baader 35nm 2" filter, both have some IR leakage so still best to use a sub aperture UV/IR filter.

On my 150mm f15 scope with only a UV/IR filter, put your hand near focus it is hot to put it mildly, no need to measure it, keep it there for a few seconds and you will have a trip to A&E.
With the Baader 35nm though as a sub aperture ERF I can keep my hand at the focal point, it has an amazing effect.
The only problem I have found with the Baader is it ads the effect of one stop to your exposures, that on my setup is about 40 FPS less, so I remove it when imaging and just go with the UV/IR.

Thirdly why use a front mounted ERF if a sub aperture one can protect you and your filter?

In my opinion it all comes down to the scope you are using.
Most people are using small lightweight telescopes because they are made to be portable, the problem here is because the tube is made to be as narrow as possible to cut down on size and weight, the inside of this tube, especially in a refractor, becomes a reflective surface, scattering unwanted light and hence lowering contrast. To combat this these narrow tubes are fitted with matt black light baffles, here lies the problem, the baffles are great heat absorbers.
You have to remember the light beam has no heat, only energy in the form of light until it is impeded then that energy is converted from light to heat.
So the baffles heat up and then cause internal tube currents that then spoils your image, so the front mounted ERF has its advantages.
If you gain an advantage without the front mounted ERF when stopping down your refractor this is most likely because the light cone is now much narrower and misses the internal baffles so no or very little internal heating.
I would say to this, if you are confident and only use the scope for solar work try removing the internal baffles and see if that makes a difference, they can always be put back.
Now you may be asking why I don't use a front mounted ERF, that comes down to the way my refractor is designed, it is a professional observatory instrument and is of the Coude design, where the light path goes through the declination axis and then down the polar axis to a fixed eyepiece.
It weighs in at well over a Ton so not portable. The design uses a different principle to light baffles, it has none, instead it has a very large diameter tube, so any light hitting the side walls reflects off at such an angle it doesn't get to the eyepiece.
One of its main jobs was to project the sun all day long.

One thing that does interest me is why no one is crying out for a front mounted ERF for a Hershel wedge as most of the scopes they are used on will suffer the same problem, no body seems to be considering the improvement they could make on the image and also reduce the light so no need for a rear filter after the wedge.

My opinion is you should keep it whilst using your refractor even if it only makes a small difference, you'll miss it.

Cheers Rod


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Re: Sell the Aries DERF or not to sell?

Post by Starry Jack »

Thank you, Rod. Sage advice and very informative.

I have no idea about the Rod Wedge Conundrum.

:)
Jack


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Re: Sell the Aries DERF or not to sell?

Post by EGRAY_OBSERVATORY »

Additional to what Mark has said, Rod confirms what I have just done and have both 1.25" and "2 Baader UV/IR filters (the 2" being used with the new S-W 2" diagonal on the Sky-Watcher 'Esprit' 80ED.

Quite definitely for scopes over 80mm these are mandatory and for long-observing-times, even the 80mm scopes should be fitted as such to protect the Quark etc.

I was advised to only get Baader, as there may be others of lesser quality and safety...

I've had no problems with any heat building-up anywhere, even though along with the Ha and Cal-K on the same mount are or can be pointing directly at the Sun for several hours (like the 5th and 6th)...

The only other snag if trying now to get UV/IR filters by Baader, is there appears to be a shortage and I got the last two from one supplier around three weeks ago.

Rod also brings-up other interesting and important points too...

Best wishes
Terry


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Re: Sell the Aries DERF or not to sell?

Post by DeepSolar64 »

I have wondered about ERFs on Herschel wedge equipped refractors, especially larger ones. Would they help? Another thing comes to mind. Those old screw in eyepiece solar filters, the ones that often came standard with older refractors back in the 1970's and early 1980's. Some people had them to shatter from thermal shock which made them dangerous. Back in the 1970-1980s I used one with my old 60mm Traq refractor without issues and it often gave sharper images than any filter I ever used excepting the Hershel wedge. Would an ERF make those filters safe to use by blocking the heat BEFORE it reaches the SUN eyepiece filter?

James


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Re: Sell the Aries DERF or not to sell?

Post by Starry Jack »

I had thought the Baader white light solar film be an appropriate ERF.


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Re: Sell the Aries DERF or not to sell?

Post by MalVeauX »

Hi,

Since you already have it, I would keep it. You can have a mounting cell 3D printed to make it work on any scope. Sure you can go sub-aperture, it does work, but full aperture is superior. Again, you already have it, so I would hang on to it and put it to use. It will matter more when the maximum is here and you find yourself trying to do solar all the time and your equipment gets lots of sun time. Personally I can manage with a sub-aperture (50mm, 2") DERF with 120mm or less. But over that, I strongly suggest a full aperture front mounted DERF. So if you are using a 5~6" scope, I would absolutely keep the Aries DERF.

Very best,


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Re: Sell the Aries DERF or not to sell?

Post by DeepSolar64 »

Starry Jack wrote: Tue Sep 07, 2021 12:31 am I had thought the Baader white light solar film be an appropriate ERF.

Baader AstroSolar Film is a filter itself. It needs no ERF. It needs no other filter behind it either.

JP


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Re: Sell the Aries DERF or not to sell?

Post by Valery »

Another facts to think about:

1. Quark's blockers have a very wide range of peak transmission - from about 35% to 70%.
It will be a poor surprize when the replacement has only 35-40% transmission instead of former 70%. It can be vise-versa too :) .

2. a 35nm Baader is not 100% reflective and not 100% transparent. It absorbs at least about 20% of incoming light. Solar radiation is about 25-50x dense at the surface of the subaperture 35nm Baader (depends where one placed it in a light cone). 20% absorbtion gives about 5-8x more energy than under unfocused direct sun illumination. All this energy then dissipate as radiation (in IR) and air heating - an air turbulence right in the light cone. This turbulence has a very small scale but it is here, it makes images soaper and Lucky Imaging technique can't fight against such internal seeing distorsion. Final images are always somewhat less clear than taken with a front DERF.

An internal DERF in a large refractor should be at least 55-70% of the aperture diameter and should not be made of a red glass with an IR coating. It must be fully dielectric and of a better optical quality than a front DERF.

Valery


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