Bloop tube: help visual acuity and sight pic?

ABoyd57946 · Post by **ABoyd57946** » Sun Jun 23, 2013 6:38 pm

Greetings,
I am a improving smallbore shooter with a question re bloop tubes? Do they sharpen/improve your sight pic and visual acuity?

Background summary - I have vision correctable to 20/40 to 20/30 in my shooting eye. My scores on the 50 meter target are poor 145/200 today. However on my SCATT my average is a 9.5 per shot and on a 40 shot practice today using NRA rules with a 20x scope I fired a 376/400 in the wind. My typical scope scores over the NRA course are 390-392 on the 50 meter and high 390s on 50/100 yd stages. In a scope match 2 weeks ago I shot a 1548 with a 10 shot dumb mistake penalty in a fishtailing 5-10 mph wind.

So while I know I need more position work do I buy a bloop tube with my .5 diopter or just focus on the any sight matches and bin any hopes off shooting under intl rules? I do like the 50 meter courses but if I can't do it anymore then I have to face reality. Any honest thoughts welcome. My goal was/is the Dewar Team or an intl match one day.

Thanks, Tony

KatoomDownUnder · Post by **KatoomDownUnder** » Mon Jun 24, 2013 1:23 am

A sight extender may help but the main purpose for these bits of kit is to reduce your sight radius. Some such as the Starick Tube and Eric Uptagraff's tubes can also be used as barrel tuners.
I would strongly suggest speaking to an optometrist with experience with shooting lenses.
Someone here should be able to recommend one near your way.

Tim S · Post by **Tim S** » Mon Jun 24, 2013 2:07 am

A tube can help if you are long sighted, but a good optician can prescribe a lens to keep the foresight sharp.

ABoyd57946 · Post by **ABoyd57946** » Mon Jun 24, 2013 7:08 pm

Thanks to all for the feedback. Re the front sight I can see that perfectly well. My problem seems to be the great amount of astigmatism I have. The bull seems distorted somewhat and fuzzy. Does this change anyone's assessment?
Please do let me know.

FYI more background. Re medical care I am blessed to live near one of the best vision centers in the entire USA and I have two specialists there. The one who did my contacts was the best lens fitter in the Midwest. So my glasses are the best that can be hoped for by anyone.

Thanks again for the help and kind regards.

ShootingSight · Post by **ShootingSight** » Mon Jun 24, 2013 8:14 pm

OK, so here is some advice you can take to your optometrist to get a lens fitted:

Your goal is to have your relaxed focus fall at the hyperfocal distance of the front sight, so that your depth of field is evenly split between the front sight and the target. Print this out and take it to your doc, he will instantly understand what you are trying to do.

The hyperfocal distance is 2x the distance from your eye to the front sight, and will require a lens which is +0.50 diopters added to your best distance vision lens.

Getting your focus to this point, combined with a small aperture for depth of field, will give you the best possible shooting vision.

Regarding your question about bloop tubes - yes it can help you, because it moves the front sight further from your eye, reducing the amount of depth of field you need to see the sight and the target together, clearly at the same time. 6" might not seem like a lot, but lens math is all based on inverse distance, so a difference between a 27" sight radius and a 33" sight radius will make almost 1/4 diopter difference in your hypewrfocal distance.

Feel free to get in touch, or have your doctor get in touch if he wants to discuss the optical math more.

Regards,

Art Neergaard
ShootingSight
513-702-4879

Tim S · Post by **Tim S** » Tue Jun 25, 2013 3:56 am

Extension tubes won't do anything for an astigmatism. All they do is to place the foresight further away. The only way to correct for an astigmatism is by a prescription lens.

KatoomDownUnder · Post by **KatoomDownUnder** » Tue Jun 25, 2013 6:35 am

Tim S wrote:Extension tubes won't do anything for an astigmatism. All they do is to place the foresight further away. The only way to correct for an astigmatism is by a prescription lens.

Tim is spot on. You need to get a shooting lens made to suit both your astigmatism and focal length. As someone with both issues one thing you need to do if and when you get some shooting frames is to make sure you set the lens up for your astigmatism whilst in position behind your sight so as to ensure its spot on.
Your optometrist should be able to show you how this is done, it's actually very simple but vital to get the best out of your lens.

ShootingSight · Post by **ShootingSight** » Tue Jun 25, 2013 7:02 am

Tim S wrote:Extension tubes won't do anything for an astigmatism. All they do is to place the foresight further away. The only way to correct for an astigmatism is by a prescription lens.

Agree 100%, and sorry if I was not more clear on that. The +0.50 you want in a lens is to be added to your best vision correction lens (which includes the astigmatism correction). When you look at your distance prescription, it will have three principal numbers for SPHERE, CYLINDER, and AXIS. You would add +0.50 to the SPHERE value, and keep the other two values (which correct your astigmatism) unchanged.

ABoyd57946 as guest · Post by **ABoyd57946 as guest** » Tue Jul 09, 2013 5:36 am

Hello all,
I read and re-read all your posts. Thank you kindly for all your replies and technical advice. I have a follow up question. I was wearing contacts before when I posted my previous results. I have a pair of Knobloch glasses with my proper distance and astigmatism correction in the lens. My 0.5 diopter front sight lens blurs the sight pic somehow. Testing this a second time with my knobloch glasses gave slightly better results. Specifically when I acquired and held a good sight pic, I shot 8-9s with one 10. When I lost my sight pic my elevation was on call but my windage was quite wide.
Q - Anschutz sells a rear 1.5x diopter with color filter lens/adjustable iris setup at Champions Choice in the US for the rear sight. While not ISSF legal, would this add the +0.5 diopter power and thus give me the best possible combo to shoot metallic sights? A similar Gehmann setup w/o the diopter works well in tough lighting for me when I could see the target normally. Based on the replies I got it seemed like it may. Just wanted to get feedback before I spent a lot of $$ on either a new lens or the Anschutz setup.

Thanks again.

ShootingSight · Post by **ShootingSight** » Tue Jul 09, 2013 7:07 am

Adding a front +0.50 diopter will blur the target. A positive diopter brings your focus closer (further from the target), however it also magnifies by about 1.5X. The fact that a lot of people use a front +0.50 is that they feel the magnification benefit outweighs the focus negative.

The adjustable diopter will do the same thing for you, it also provides a 1.5x magnification, but has an adjustable focus, so you can dial it to restore the balance of focus to be between the front sight and the target.

Centra and Gehman both make adjustable diopters.

Guest · Post by **Guest** » Thu Nov 14, 2013 9:15 pm

Hello all. I wanted to provide an update and say thank you to all who provided feedback. Re my problem, I added a 10 inch tube, increased my front aperture size to 4.5 mm, and through color filters and adjusting the rear iris I can obtain a sharp sight pic again. I have to shoot quickly in the aim but my results are 9.3 to 10.2 decimal when I execute properly. Thank you all again. Sincerely, Tony

Rover · Post by **Rover** » Thu Nov 14, 2013 10:27 pm

The real question is: Did you get your astigmatism fixed?

Tim S · Post by **Tim S** » Fri Nov 15, 2013 4:01 am

Rover wrote:The real question is: Did you get your astigmatism fixed?

He already had a prescription lens which accomodated his astigmatism, and post as such (read reply no. 8).

Pat McCoy · Post by **Pat McCoy** » Fri Nov 15, 2013 5:39 pm

When you get ready to do testing of changes, spend few dollars on a larger (7.0) front aperture insert, and see how it helps your scores.

If you decide to do this, we would all appreciate your results.

bpscCheney · Post by **bpscCheney** » Fri Nov 15, 2013 10:33 pm

When I use anything bigger than a 5.3 front diopter on my 10 inch tube I start to lose my ability to center it, but that's just my opinion. 5.3 works well with a standard barrel plus tube (I went with a 4.0-6.0 front aperture).

Guest · Post by **Guest** » Thu Nov 21, 2013 9:54 am

Re aperture size there is a fantastic article on the USA Shooting website written by Marcus Raab. The article is about applying aiming theory to practice with aperture size. In the article are instructions on how to determine the minimum size aperture for use. My rifle is a Ans 1907 and applying the theory led me to the 4.5 mm size. I get a fine line of white pic that is almost textbook. I highly recommend it.

And Marcus if you are reading this thank you for sharing your expertise.

bpscCheney · Post by **bpscCheney** » Thu Nov 21, 2013 4:25 pm

+1 to Marcus Raab on that article, it actually helped me narrow down my selection for apertures, and he's an Alumni from my school :)

Pat McCoy · Post by **Pat McCoy** » Thu Nov 21, 2013 9:16 pm

The article Marcus wrote was excellent for determining MINIMUM aperture size.

Many are moving to much larger sizes (for standing especially) with better results. Inserts are inexpensive. Don't be afraid to experiment.

TargetTalk

Bloop tube: help visual acuity and sight pic?

Bloop tube: help visual acuity and sight pic?

Bloop tube / sight extender

Astigmatism