Jump to content

 

1825338873_SNRPN2021banner.jpg.68bf12c7791f26559c66cf7bce79fe3d.jpg

 

Annoying imaging problem


Matthew.Blake
 Share

Recommended Posts

So, I got the Cannon 50mm f/1.8 lens for my camera and thought I'd try some almost widefield photography. Normally I can't go above 30 second exposures with my scope because the alignment and PEC aren't good enough and I'm not patient enough to sort them out. However, at 50mm I reckoned I could get away with 1 minute subs as each pixel represents that much more angle in the sky. To my delight I found I was right!

To my horror, however, 1 minute at ISO 400 F/2 is enough to saturate the sensor with the sky glow from light pollution where I live :-( Coventry sucks, the coucil won't even turn the lights off at night because they seem to think, contrary to empyrical evidence, it will increase crime and more old ladies will fall over.

Link to comment
Share on other sites

  • Replies 28
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

Posted Images

Indeed, I was amazed at the difference when I experimented by pointing my camera upwards, and resting a cheap 2" LPR filter on the skylight filter that is permanently attached to the lens. On a 3 minute exposure, the area that the LPR filter covered was still a nice, contrasty dark-grey/black, and the outlying area was, yep, orange-mush. I'll post the pi©s later when I get home from work.

Link to comment
Share on other sites

anyone know where I can pick up a 52mm LPR filter?

The B+W #491 "Redhancer" (didymium glass) is nearly as good, it blocks sodium glow just as effectively as the CLS filter, but it doesn't clobber mercury vapour lamps too.

Link to comment
Share on other sites

You can get a reducing ring to fit the 2" SW LPR filter nicely. The lens is quite narrow, much narrower than the 2" filter so you shouldn't get vignetting. A CLS Clip filter works great though. You do get some quite rough stars around the edges of the FOV at under f/3.2 (it wasn't great even then). I've not had a chance to try since then, so perhaps f/4 would be best.

Link to comment
Share on other sites

The B+W #491 "Redhancer" (didymium glass) is nearly as good, it blocks sodium glow just as effectively as the CLS filter, but it doesn't clobber mercury vapour lamps too.

It looks like it cuts out lots of green and blue though, or am I just misinterpretting?

Link to comment
Share on other sites

You can get a reducing ring to fit the 2" SW LPR filter nicely. The lens is quite narrow, much narrower than the 2" filter so you shouldn't get vignetting. A CLS Clip filter works great though. You do get some quite rough stars around the edges of the FOV at under f/3.2 (it wasn't great even then). I've not had a chance to try since then, so perhaps f/4 would be best.

Any idea where to get one?

Link to comment
Share on other sites

I got a 52mm to 48mm ring from ebay I think... I know psychobilly has posted somewhere to get reducing/stepdown rings from... I can't find a 52to48... I'll have to dig mine out and check the details on it later.

Link to comment
Share on other sites

I just checked, it's defo a 52mm to 48mm step down ring... on my searches I could find 52-49 and 52-46 but not 52-48... it's probably worth you having a search though...

either as a step ring, stepping ring, stepdown ring, or reducing ring... something like that.

Link to comment
Share on other sites

It looks like it cuts out lots of green and blue though, or am I just misinterpretting?

The Redhancer was designed to work with film cameras ... colour transparency films contain layers sensitive to red, green and blue, and the red & green tended to overlap a bit (in the yellow). The Redhancer removes this overlap, making the differentiation between green foliage and "autumn colours" much better defined. Transmission in the green & blue is over 80% ... Trust me, it works, it's a narrowband notch filter centred on the sodium D lines.

Link to comment
Share on other sites

I had this problem too but with so many different lenses with different sized filter threads it could have got really expensive buying a filter for each lens.

In the end I went for the Astronomik CLS CCD clip in filter which goes into the body of the camera, you cant use EF-S lenses but the EF lenses work a treat, and now I can use one filter with all my lenses.

Link to comment
Share on other sites

That EOS clip filter looks like the one for me. I sold my 18-55mm EF-S kit lens to part-fund my one multi-purpose lens, a Tamron 18-270mm zoom, which I'm pretty sure has enough rear clearance to use the clip-on. The only thing that protrudes beyond the bayonet flange is the seven-copper-contact mount, about 2 - 3 mm in height. Can anyone who uses the clip-on say whether I might have clearance issues or not? Also, my 500D is conspicuous by it's absence from the "Will fit these cameras" list... :o

post-17238-133877489017_thumb.jpg

Edited by Takahashi
Link to comment
Share on other sites

This is the wee experiment I carried out by planting a standard SW LPR filter on the camera lens and opening the shutter for three minutes on the EQ6. Quite a staggering difference between the filtered centre-circle and the unfiltered periphery.

post-17238-133877489022_thumb.jpg

Link to comment
Share on other sites

This is the wee experiment I carried out by planting a standard SW LPR filter on the camera lens and opening the shutter for three minutes on the EQ6. Quite a staggering difference between the filtered centre-circle and the unfiltered periphery.

Awesome, just pure awesome! I'll be giving that a go!

Link to comment
Share on other sites

You'll be fine with that lens and the clip in filter, the EF-S lens has an extra rubber/plastic ring that protrudes a further 3mm beyond the contacts panel.

I can take a piccy of both lenses if you would like to see.

Here ya go, EF-S on the left, EF on the right.

post-17668-133877489035_thumb.jpg

Edited by simon84
Link to comment
Share on other sites

Thanks Si, most valuable info. :o

Feel free to send piccies... any reference is a help.

The optimist in me is telling me the only reason the 500D isn't on the compatibility list of the retailers I've checked, is down to them not updating said lists, yet. :)

EDIT : Ah, yes... quite a difference.

Edited by Takahashi
Link to comment
Share on other sites

It does seem to be a bit pointless that extra ring. My one has a rubber ring around it which can be removed so I'm guessing its only for guiding purposes, or maybe to remove any vibration in the lens when the mirror swings up. Not too sure.

The only thing I'm missing out on is being able to use my CLS filter at 18mm, my next widest setting I have is 28mm on my EF lens.

Link to comment
Share on other sites

Just been looking around for a solution to the EF-S lens problem and found this, 7dayshop.com - Online Store

Not a cheap solution but will give that much needed to space to allow all EF-S lenses to work with clip in filters........I guess at the end of the day it all depends how much you really need to use an EF-S lens for your widefield imaging.

For me it gives me access to 18mm so probably well worth the £59, but then saying that if Canon make one I'm sure someone else makes something like this aswell......I'll keep looking.

Edited by simon84
Link to comment
Share on other sites

I've just ordered a reducer ring that will allow me to attach the 48mm thread astro filters onto a 52mm thread. It was only £2.50 and there were all sorts of other sizes available so, once I've tested it, I'll probably get one for every lens I buy.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.