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The SCT Rear Port Skylight Filter/Dust Seal

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16 replies to this topic

#1 clamchip

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Posted 13 March 2019 - 11:29 AM

This product seems like a good idea to me, am I missing something?

It's been discontinued by everybody:

Celestron:

https://www.bhphotov..._Seal_for.html 

Meade:

https://www.bhphotov...ght_Filter.html

Lumicon:

https://agenaastro.c...eal-lf3155.html

GSO:

https://agenaastro.c...-dust-seal.html

Maybe it doesn't work well with modern imaging? 

Is it now a classic we must go hunt the used market to find one?

Maybe it reduces precious light too much for astronomy? 

When I did  film years ago I always kept a Skylight filter on my lens to protect it.

Keeping dust out and off the primary and especially the secondary is a great idea.

Not to mention the other benefits listed for this Skylight Filter/Dust Seal. 

IT sure would help preserve our old SCT MCT coatings, or is it better to introduce

some outside air once in a while? the coatings have lasted pretty well in my oldest

from 1975 but still there is some loss of reflectivity from age I'm sure.

 

Robert


Edited by clamchip, 13 March 2019 - 02:10 PM.


#2 petert913

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Posted 13 March 2019 - 11:52 AM

I would prefer clear, coated glass.  But looks like a good idea.



#3 clamchip

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Posted 13 March 2019 - 01:33 PM

I found this page, but it's camera and daytime, not highpower night time telescope:

https://www.bhphotov...ters-for-lenses

 

Robert



#4 Jeff Lee

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Posted 13 March 2019 - 01:48 PM

I only use my C8 @ f10 for very small stuff when doing EAA, always has a FR6.3 or 3.3 on it.

#5 clamchip

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Posted 13 March 2019 - 02:23 PM

I have one of these, it came with my recently purchased black tube C8.

I'm pretty sure it is the Celestron 93621 because the knurl seems to

match in all the pictures I've seen:

https://www.bhphotov..._Seal_for.html 

It took me a while to find out what it was but I narrowed it down to this

Skylight 1A filter.

I removed it because it had the most beautiful text book fingerprint right

smack in the middle of it. And also because I don't really like anything

in the optical path unless its absolutely necessary. 

I did clean it and holding the filter up to peer through during daytime I see 

a increase in contrast. 

So that's +2, protects the OTA and a possible increase in contrast.

 

Robert


Edited by clamchip, 13 March 2019 - 02:31 PM.


#6 starman876

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Posted 13 March 2019 - 03:22 PM

I like them to keep the SCT sealed so dust never enters the system.   Looks like I better hang on to the ones I got.


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#7 clamchip

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Posted 13 March 2019 - 08:21 PM

Here's the 1998 Celestron accessories catalog and on page 17 is the unit we are discussing:

http://celestron.ru/...sories-1998.pdf

 

Still, I'm completely mystified (not fossilized like my wife say's I am) about the fact everyone

has dropped this gadget like a hot potatoconfused1.gif

Well, I'm going to run it thru the mill and see what gives.

 

Robert


Edited by clamchip, 13 March 2019 - 08:26 PM.


#8 telesonic

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Posted 13 March 2019 - 10:07 PM

It sure seems like a good idea Robert, and I thought I had seen these for sale - but you are right, they are no longer available and that is interesting. I know for a fact that the big C had 1A thread in filters in .965 and 1.25, I have an older MIJ one that I had almost forgot about. 

 

As for finding one, I know of two sources - one out west, and one out east that are known to have a bunch of NOS stuff. 

 

 

Maybe it reduces precious light too much for astronomy? 

 

Perhaps. grin.gif  

 

Looking forward to what you find on this, planning on any imaging with it?

 

T



#9 clamchip

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Posted 14 March 2019 - 10:21 AM

I'm hopping to use the C8 for imaging, I bought it because it's Fastar compatible and

I want to try out the f/1.95 speed.

Unfortunately the Fastar and Hyperstar lenses are pretty expensive, and the camera

that attaches to the lens.

Apparently the Fastar lens works best with small chip cameras, it's been obsolete now

for quite a while.

I don't really want to buy 20 year old imaging gear but I may be able to buy something

affordable if someone is up grading. I can then get my feet wet. Normally I live in the

old world and buy old stuff but the imaging equipment has come a long ways in 20

years.

Celestron started adding the Fastar port around 1994 so there is some old equipment

out there.

 

Robert   


Edited by clamchip, 14 March 2019 - 10:29 AM.

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#10 mich_al

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Posted 14 March 2019 - 01:05 PM

It will get in the way of a Lymax cooler.



#11 clamchip

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Posted 14 March 2019 - 04:18 PM

Now we have :

+1 protects the optical tube

+1 visible increase in contrast during daytime

 

-1 possibly a reduction in the throughput of the system

-1 it will be in the way if using a tube cooler

-1 you cannot use a film canister to plug the visual back

-1 added source of reflections from bright objects

 

I hopefully will get to test it celestially soon and there I may see the reason(s) why

this filter/ dust seal is no longer popular.

I'm not a astro photographer or imager so I will not be able to perform tests here.

 

Robert


Edited by clamchip, 14 March 2019 - 06:07 PM.


#12 davidmcgo

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Posted 14 March 2019 - 05:07 PM

I add another minus for added source of reflections of bright objects in the field of view.

 

Dave


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#13 clamchip

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Posted 14 March 2019 - 06:08 PM

I add another minus for added source of reflections of bright objects in the field of view.

 

Dave

I'll add it to the list.



#14 mich_al

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Posted 15 March 2019 - 08:50 PM

Also will trap moisture which makes fungus happy.  I bought one for my C9.25 to keep dust out but haven't used it in years.  Seemed like a good idea at the time.


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#15 clamchip

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Posted 16 March 2019 - 10:06 AM

It looks like we are piling up a lot of negatives.

And now I've got pollen.

I might hold off on testing.

 

Robert



#16 Kasmos

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Posted 16 March 2019 - 11:01 PM

Don't you cap the back when you don't use them?


Edited by Kasmos, 16 March 2019 - 11:01 PM.


#17 clamchip

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Posted 16 March 2019 - 11:07 PM

When I bought my C8 the filter was screwed on to the rear port and then capped.

I got the impression you left the filter/dust seal on permanently.

 

Robert 




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