Picking and Using a Barlow (1 Viewer)

Paul Corfield · Feb 10, 2013

JGobeil said:
Hello Paul,

I will thy this with my GSO barlow. What is the minimum aperture that can be used without having to reduce shutter speed ?

Thanks
Jules

Try about 15mm or 20mm. You will see vignetting before the shutter speed needs to be adjusted, no matter how small the aperture goes there doesn't seen to be any loss in light. I guess most of the glass in the diameter of the barlow is just wasted.

Paul.

rferrieri · Feb 11, 2013

cabin fever

I am getting cabin fever with 2 ft of snow outside my door. I was inspired by some of Paul's comparison shots of a TC to a barlow and thought I would run some tests comparing my Olympus x1.4 TC (7 element assembly) with a 2" GSO ED barlow mounted inside the camera adaptor. I ran out of daylight so shot my neighbor's porch lamp through my bedroom window. Not the best test, but interesting. Both shots were made at iso 400, 1/200sec on my f/5 scope. The TC was slightly resized. Similar light throughput in each shot--at least to my eyes. If you look at the cropped view of the cedar shingles, the barlow showed more detail of the fine texture in the shingle. I am in the process of making a 20mm baffle and will position that in front of the barlow. tomorrow I hope to take some daytime shots. Everything on Long Island is still shut down from the storm's aftermath and the forecast is for freezing rain on top of that. Rich

JGobeil · Feb 11, 2013

Paul Corfield said:
Try about 15mm or 20mm. You will see vignetting before the shutter speed needs to be adjusted, no matter how small the aperture goes there doesn't seen to be any loss in light. I guess most of the glass in the diameter of the barlow is just wasted.

Paul.

Thanks for the info Paul. I made a disk with a 15mm aperture and will test it today or tomorrow.

If anybody is interested, I made the disk with plastic from a DVD box, the kind used for movies. It is made with thin black matte plastic and is easily cut with scissors. I used a 5/8 inch spade drill bit to drill the center hole. You will get a clean cut by running the drill at high speed and going in slowly, with the plastic sheet robustly attached to a wooden block. With the right diameter, the threads inside the front of the barlow will hold the disk in place.

Regards
Jules

FineArt · Feb 15, 2013

Paul Corfield said:
No idea, all I know is it disappears once the aperture is reduced. A 2" barlow can be stopped down to around 10mm before any vignetting is noticed. Image sharpness is unaffected and contrast/saturation is greatly improved.

Paul.

I bought a barlow. Of course it has what Paul warned us about. I will have to mask it.

DanC.Licks · Feb 15, 2013

I picked up a Minolta MC Rokkor 100-200mm/5.6 and tried the TN out of it. Basically crap. Poor contrast and not all that sharp. Nowhere near as good as my Cannon TN or the Sunagor.
I also got a Celestron Ultima SV 2x Barlow (1 1/4"). Haven't really had time to try it out (got too dark) but it seems that it is better "right side up".

DanC.Licks · Mar 20, 2013

I got a Nikkor TC 301 (2x) to go with my Nikkor 400mm/5.6 ED IF, and tested it against my Canon TN, both on the scope and on the 400.

Just a rough test, but enough to tell me that the TN still kicks ass on the scope, but that it is not good on the 400mm. Also the SW basically blows the Nikkor out of the water, albeit, the Nikkor is a BIT easier to carry around.

Paul Corfield · Mar 20, 2013

TN's don't seem to work well behind a regular camera lens when compared to a TC. I guess both are designed to do different things. In a camera lens the TN sits just behind the objective and on the scope it's mounted the same way. I guess it's design just too specialized to do anything else although they work well as barlows on eyepieces.

Paul.

DanC.Licks · Mar 20, 2013

I also tested my Barlow. Couldn't even come close to the TN!

JGobeil · Jul 16, 2013

IQ with and without a barlow

I use my telescope only for birds that are too far for the OM-D with the 100-300mm lens. I was wondering what is better for long range photography: using the barlow or crop without the barlow to get the same image. I made the test, here are the results:

Olympus OM-D EM-5
2" camera adapter
GSO 2X ED Barlow
2 x 50mm extension tubes
Sky-Watcher 80ED

The barlow is mounted at the end of the camera adapter and has a 15mm baffle mounted inside the barlow housing, on the scope side.

The photos received the normal processing I usually do in LightRoom and Photoshop.

Increase clarity and/or contrast
Adjust exposure
Reduce noise
Sharpen moderately

#1: No gain photo taken with a 12-50mm Oly lens set at 25mm (50mm eq.). The red circle shows the target, distance 83 meters.

#2: Photo taken without the barlow. No cropping - down sized to a width of 1000 px - ISO 800 - 1/600 s.

#3: Photo taken with the barlow. No cropping - down sized to a width of 1000 px - ISO 800 - 1/500 s.

CONTINUED IN THE NEXT POST

JGobeil · Jul 16, 2013

IQ with and without a barlow (continued)

#4: Same photo as #2 (no barlow) cropped to 32.5% of the original - 1498/4608 px

#5: Same photo as #3 (with barlow) cropped to 56.6% of the original - 2608/4608 px - to show the same image as photo #4

#6: Same photo as #2 (no barlow) cropped to 3.2% of the original (upper bolt and washer) - 146/4608 px

#7: Same photo as #3 (with barlow) cropped to 5.5% of the original - 2608/4608 px - to show the same image as photo #6

If you look at the moderate crops, photos #4 and #5, there is not much difference in IQ. This shows that the scope provides very good resolution with room for quite a bit of cropping, with or without barlow. However, if you crop more (way too much !) we see that the photo with the barlow has a clear advantage. IMO, a barlow is not needed before 50-60 m. - after that, I will try to use the barlow but, in a hurry, I can still get interesting images without it.

Regards
Jules

Paul Corfield · Jul 16, 2013

I found the same as you Jules. There is a distance that scope + cropping works well up to and then beyond that it's best to magnify with a barlow, telenegative or teleconverter. Sometimes though, poor air quality can mean it's just best to crop no matter what the distance.

Paul.

JGobeil · Jul 17, 2013

Paul Corfield said:
I found the same as you Jules. There is a distance that scope + cropping works well up to and then beyond that it's best to magnify with a barlow, telenegative or teleconverter. Sometimes though, poor air quality can mean it's just best to crop no matter what the distance.

Paul.

Thanks for your comments Paul. The way I see it, when there is a lot of haze and heat waves, no matter what equipment you use, long shots will be bad !

Anyway, with this wx, I tend to stay home... Just like the last 7 or 8 days here. 32 C. and very humid. Nor good nor pleasant for birding. :C

I'm amazed at the IQ of this scope, with and without barlow. It is just like a big white cannon with and without a 1.4X TC. What I like less is the f/7.5 ratio, the narrow depth of field and of course manual focus. Well, for 12K$ less, I'm willing to live with that...

Regards
Jules

Paul Corfield · Jul 17, 2013

Similar weather here in the UK at the moment, very hot start to the summer and averaging around 25-30 deg C for a couple of weeks now. Maybe a thundery breakdown for us next week. I should be moving house in a couple of weeks and that will free up some funds to finally replace my broken Canon 450D. I'm more of an autumn/winter/spring photographer so there's no big hurry and I don't miss it too much at the moment.

Paul.

JGobeil · Jul 17, 2013

Paul Corfield said:
Similar weather here in the UK at the moment, very hot start to the summer and averaging around 25-30 deg C for a couple of weeks now. Maybe a thundery breakdown for us next week. I should be moving house in a couple of weeks and that will free up some funds to finally replace my broken Canon 450D. I'm more of an autumn/winter/spring photographer so there's no big hurry and I don't miss it too much at the moment.

Paul.

Well, good news and bad news ! That's life...

Tord · Jul 22, 2013

I have not yet come to use Barlows since I already have TC which are capable of delivering good results with the SW. As rule of thumb I will use have TC 1.4 (2.0) to have the anticipated subject cover 1/4 of the frame (50% crop), pending light conditions.

DanC.Licks · Jul 22, 2013

The EC14 performs pretty well on the SW, but the EC20 does not. Too soft. I got better shots up-resing EC14 shots to the same size as EC20 shots. But my home made telenegative is still a cut above the EC14.

Picking and Using a Barlow (1 Viewer)

More options

Paul Corfield

Well-known member

rferrieri

Well-known member

Attachments

JGobeil

Nature Photographer

FineArt

Well-known member

Attachments

DanC.Licks

AKA Daniel Bradley

DanC.Licks

AKA Daniel Bradley

Paul Corfield

Well-known member

DanC.Licks

AKA Daniel Bradley

JGobeil

Nature Photographer

Attachments

JGobeil

Nature Photographer

Attachments

Paul Corfield

Well-known member

JGobeil

Nature Photographer

Paul Corfield

Well-known member

JGobeil

Nature Photographer

Tord

Well-known member

DanC.Licks

AKA Daniel Bradley

Similar threads

Users who are viewing this thread