Does this adapter exist?

[Brent]

i have only 7mm inward focuser travel available but I want to add a Skywatcher light pollution filter to my imaging train. (I can't use a clip as it's a Sony DSLR)

The only way I can think of doing it is to buy the 2" filter, screw it into the 2" thread of the T-ring, then screw the step down piece (it's a 1.25" focuser) from the centre of the T-ring back into the filter.

Unfortunately, this would require the filter having to support the camera weight which isn't a great idea, I know.

I contacted FLO and a fast reply informed me that the filter body is about 4mm deep but that the threads may not be long enough to stably support the camera weight.

Does anybody know of a VERY low profile adapter that might work to screw the filter into and thus protect it from the camera weight? Is that an impossible adapter design wise? I'm finding it difficult to get my head around!

Or is my only option to try the direct connection above and use some thread lock as a permanent solution?

[Tinker1947]

Can you put a 1.25" filter in the step down piece....

[Brent]

Can you put a 1.25" filter in the step down piece....

Unfortunately not, it's an M42 thread.

Edit:

Sorry Tinker1947, I don't think I made myself very clear. I forgot to mention that I don't use a T-adapter as it needs a barlow to come to focus.

The step down piece I mentioned is part of the T-ring.

[Steve Ward]

So put an 1-1/4" filter on the front of the Barlow .... 

[Brent]

So put an 1-1/4" filter on the front of the Barlow .... 

That would definitely be possible but I thought I'd read not to use a barlow for deep sky imaging? Can't remember who, but I was sure I saw a prominent imager post it was a no-no. Maybe I got the wrong end of the stick.

Also, would it introduce chromatic abberation or is that just down my 2x barlow being poor quality? I tried it on the moon with the DSLR Sunday evening and had fairly bad colour fringing on the edges. Was that just because the moon is so bright?

I suppose the other reason I didn't want to use a barlow is that I wouldn't be able to fit a coma corrector in the train. I would probably have to crop even closer. But then, am I wrong with that? Would a coma corrector move the focus point further out?

[Steve Ward]

OK ... but surely a part of the adapter fits inside the 1-1/4" focuser ... ?

The filter would screw onto the front end of that ... ?

Maybe a picture of the bits and bobs would help us ... 

[Brent]

Just got back in - thanks for helping Steve.

OK ... but surely a part of the adapter fits inside the 1-1/4" focuser ... ?

The filter would screw onto the front end of that ... ?

Maybe a picture of the bits and bobs would help us ... 

Yes, you are right of course. I should have done that at the start.

So, first shot is the camera with T-ring attached, second shot is the focuser with the eyepiece adapter removed, third shot is the two mated.

This is how I've been imaging up until now, it leaves just 7mm of inward focus.

[DoctorD]

Hi Brent

A Barlow is not usually recommended for DSO photography as it increases the focal ratio extending exposure time needed.

Have you considered moving your primary mirror up the OTA giving you a bit more focus travel - this is often recommended for newts?

HTH

Paul

[Xplode]

The Baader protective T ring with a 2" filter is the only way i know that this can be done easily. It's costly, but it allows you to use the full aperture M48/2" at a later point if you buy another scope 

[Xplode]

Just remembered Baader only have a version for Canon's so it won't work after all

[Chris Rowland]

I've heard that you can get low profile T rings, would that give a bit more room to play with?

Chris

[bogdog]

my reply on this topic might be helpful might not

http://stargazerslounge.com/topic/210887-is-there-such-a-thing-as-this-adaptorfilter-holder/

[Brent]

Thanks everyone, had a busy few days so not had chance to reply until now.

Hi Brent

A Barlow is not usually recommended for DSO photography as it increases the focal ratio extending exposure time needed.

Have you considered moving your primary mirror up the OTA giving you a bit more focus travel - this is often recommended for newts?

HTH

Paul

Thanks Paul, couldn't remember the reason.

I think I'd need to move it at least an inch which I don't think would be possible within it's current collimation reach, might have to try longer screws. I'm loathe to shorten the tube though 

The Baader protective T ring with a 2" filter is the only way i know that this can be done easily. It's costly, but it allows you to use the full aperture M48/2" at a later point if you buy another scope 

Just remembered Baader only have a version for Canon's so it won't work after all

That was what I was trying to find. It would have been perfect

I've heard that you can get low profile T rings, would that give a bit more room to play with?

Chris

Hmm, interesting, although I don't think I'd get enough out of it.

my reply on this topic might be helpful might not

http://stargazerslounge.com/topic/210887-is-there-such-a-thing-as-this-adaptorfilter-holder/

Thanks bogdog. I have one of those as well as a T-adapter. The problem, though, is that I have to use the eyepiece adapter to use them and that is what causes them not to come to focus

So, to sum up for any newbie who might find this thread through search in the future, it would appear my options are:

1) Buy a Canon so I can use a clip filter (£130ish? (better filter I know) + the camera cost vs £21 for the Skywatcher 1.25")

2) Move the mirror up the tube hopefully attaining focus with longer collimation screws.

3) Use what I have with shorter exposures and process the lp out.

I think I'll give longer collimation screws a go first and see what happens.

If successful, would reducing the focal length noticeably alter the speed of the scope and make collimation harder?

[Ant]

I moved the mirror up the  by around 3/4 inch - a bit daunting but a fairly easy job once you bite the bullet and make a start.

Cheers

Ant

[JamesF]

I think I'll give longer collimation screws a go first and see what happens.

If successful, would reducing the focal length noticeably alter the speed of the scope and make collimation harder?

It doesn't reduce the focal length.  The focal length remains the same, so moving the mirror up the tube moves the focal plane "out" of the focuser by the same amount.

It won't therefore change the focal ratio of the scope and shouldn't make collimation any harder.

James

[Brent]

I moved the mirror up the by around 3/4 inch - a bit daunting but a fairly easy job once you bite the bullet and make a start.

Cheers

Ant

Thanks for the reassurance Ant. Did you need to shorten the tube or manage with longer screws?

It doesn't reduce the focal length. The focal length remains the same, so moving the mirror up the tube moves the focal plane "out" of the focuser by the same amount.

It won't therefore change the focal ratio of the scope and shouldn't make collimation any harder.

James

Ah, of course not. The focal plane moves as well, otherwise there wouldn't be much point :-)

[Ant]

Sorry to say this but I actually cut off 3/4 off the tube, re drilled the holes and replaced the mirror cell.

I did it with a metal hand saw, it would have been a quick and MUCH neater job if I had had a Drimmel.

Cheers

Ant

[Xplode]

By cutting the tube the focal plane moves, but not focal length. Focal plane will move further out from the focuser.

If you can afford it go for a Canon camera and the Baader T ring, it's a much better camera and more suitable for astro than the Sony. It will also make you able to use BackyardEOS to control imaging.

1100D is a good choice, but if you need something cheaper a 450D is also pretty good and has liveview and USB BULB.

[Brent]

I think I'm going to have to take some off the tube then

It's by far the less appealing option but there's no chance of buying a Canon and a protective T-ring for a long while. And when I do I'll be buying pre-modded and will probably get the CLS clip instead.

I'll build myself up to it over the next few days!

[Tinker1947]

Good Luck with the shortening of the tube, while its metal i would run it through my table saw taking the required amount off using a fence and a fine toothed blade, if you don't have a table saw, then maybe a piece of flat plastic strip around the end and used as a guide for a hacksaw, keeping the part of the tube being cut against something sturdy to stop the tube wobbling.....

Something like this where only the blade goes through and the saw is straight....

http://uk.farnell.com/jsp/displayProduct.jsp?sku=1389083&CMP=KNC-GUK-[removed word]-GEN-LISTINGS&gross_price=true&CMP=KNC-GUK-[removed word]-GEN-LISTINGS-OTH-IRWIN_INDUSTRIAL_TOOL&mckv=qaO4fNF3|pcrid|30890130189|plid|&gclid=CMzGxdy5mb0CFdShtAodX1gAxA

[Brent]

Good Luck with the shortening of the tube, while its metal i would run it through my table saw taking the required amount off using a fence and a fine toothed blade, if you don't have a table saw, then maybe a piece of flat plastic strip around the end and used as a guide for a hacksaw, keeping the part of the tube being cut against something sturdy to stop the tube wobbling.....

Something like this where only the blade goes through and the saw is straight....

http://uk.farnell.com/jsp/displayProduct.jsp?sku=1389083&CMP=KNC-GUK-[removed word]-GEN-LISTINGS&gross_price=true&CMP=KNC-GUK-[removed word]-GEN-LISTINGS-OTH-IRWIN_INDUSTRIAL_TOOL&mckv=qaO4fNF3|pcrid|30890130189|plid|&gclid=CMzGxdy5mb0CFdShtAodX1gAxA

Thanks for the link, that looks useful. I can borrow a Dremel so will probably use that and will create some sort of guide for it.

I have to say I'm really not looking forward to doing it. SWIMBO visibly cringed when I told her what I was planning - I had hoped she'd just tell me to go ahead and get the Canon!   Lol

[Tinker1947]

Thanks for the link, that looks useful. I can borrow a Dremel so will probably use that and will create some sort of guide for it.

I have to say I'm really not looking forward to doing it. SWIMBO visibly cringed when I told her what I was planning - I had hoped she'd just tell me to go ahead and get the Canon!   Lol

I don't think a dremal will be that easy the cutting disc's break very easily so buy a pot full and wear a face mask the bits fly every where....the hacksaw will work provided when your sawing the bit you cutting through is against some thing solid like a round piece of timber in a vice...