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I need an explanation for the "ND" in ND filters?


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Before I continue, I do know ND is neutral density. But my question.... It seems to be common knowledge that a filter of level ND 5 is needed when viewing the sun. My ND filters for my camera are ND 2,ND 4, ND 6, and so on. So can I use one of these to view/photograph the sun? If not, what is the difference between my ND camera filters and the other ND filter/film sheets everyone bought for the eclipse?

I'm sorry but I am new to any photography with telescopes. It's almost embarrassing to say it's been in storage. 

 

So, Thank you to anyone and everyone that can help!

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It goes without saying that you should never view the sun, either by unaided eye or through a telescope, except  through a filter specified for that task. 

It is essential that the filter (Baader film for example) be placed at the input of the instrument and not at the output end. The telescope is gathering a lot of light and focusing it down at the eyepeice or camera. A  filter at the eyepeice, or placed in front of a camera attached to a telescope,  will quickly become damaged by the focused sunlight .... and then go on to damage your eye or camera. 

I assume you know that neutral density filters are logarithmic in as much as ND1 means 10% is transmitted, ND2 means 1% transmitted and so on. ND5 means 0.001% of the light is allowed through. 

PS Sorry If I'm repeating what others have said but I expect a few others will post an answer by the time I hit "submit reply". 

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1 hour ago, Ouroboros said:

It goes without saying that you should never view the sun, either by unaided eye or through a telescope, except  through a filter specified for that task. 

It is essential that the filter (Baader film for example) be placed at the input of the instrument and not at the output end. The telescope is gathering a lot of light and focusing it down at the eyepeice or camera. A  filter at the eyepeice, or placed in front of a camera attached to a telescope,  will quickly become damaged by the focused sunlight .... and then go on to damage your eye or camera. 

I assume you know that neutral density filters are logarithmic in as much as ND1 means 10% is transmitted, ND2 means 1% transmitted and so on. ND5 means 0.001% of the light is allowed through. 

PS Sorry If I'm repeating what others have said but I expect a few others will post an answer by the time I hit "submit reply". 

Thank you Ouroboros, I did not know the logarithmic. It's just that many people are firm on using ND 5 to make their own filters for any optical device. And I understand that. I had a ND 5 filter I purchased and of course I could see nothing except the sun. My filters for my camera, I can. I was just wondering if the "ND 5" for scopes may be different than "ND 5" for cameras? I don't know. If it is the same then please forgive my ignorance... Also, you were not repeating what others have said. You were the first to reply(therefore the quickest), so thank you again.

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The ND 5 filters you are talking about aren't suitable for solar. A proper solar filter blocks out all light wavelengths whereas the ND 5 lets through ultra-violet and infra-red.

ND 5 does block light enough not to damage your camera but ultimately, they are not safe for visual. It's not worth the risk to either you or your equipment.

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2 hours ago, Mr Spock said:

The ND 5 filters you are talking about aren't suitable for solar. A proper solar filter blocks out all light wavelengths whereas the ND 5 lets through ultra-violet and infra-red.

ND 5 does block light enough not to damage your camera but ultimately, they are not safe for visual. It's not worth the risk to either you or your equipment.

 Thanks Mr Spock for your reply. So, not all ND 5's are created equally! But, no, I never did try that. I do value my cameras very much. That much UV & IR would fry my sensors. I guess I just couldn't figure out why they both had the same 'label' and each be different type. Kinda like calling a camera a camera. You still have to ask if it's an SLR,DSLR,Point & shoot and so on.

But, to some, who only deal with camera filters for camera lenses, it's easy to think that ND 5 is just that, ND 5, period. And since cameras and scopes are commonly used together, there really should be a better way to differentiate between the two(for people like me). 

Thank you

Edited by pixelperfect
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If you want a better way for nomenclature, logically, SND would be created for Solar and ND thus then used in normal photography. I guess that this is not the case. :)

I most certainly hope that the hype of the Eclipse did not have folk looking through bog standard ND5 filters. Manfred Mann strikes to mind "Blinded by the Light".

For me, a Novice with Solar, any filter that I can see through on a 'normal' subject, ought to be trashed before thinking about the Sun. and I can see through my ND10s before putting them on a lens.

Rich

 

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Rather than describe all ND5 as unsuitable apart from those described as "solar", the easiest way to check suitability of an ND5 is to look at the transmission curves. If it's true broadband and cuts IR and UV then it's ok, if it only cuts visual wavelengths then it is not.

The filter data sheet is your friend. If the manufacturer cannot supply a full transmission data sheet the filter should be regarded as *not* suitable irrespective of what a supplier tells you.

AndyG

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5 minutes ago, 101nut said:

Rather than describe all ND5 as unsuitable apart from those described as "solar", the easiest way to check suitability of an ND5 is to look at the transmission curves. If it's true broadband and cuts IR and UV then it's ok, if it only cuts visual wavelengths then it is not.

The filter data sheet is your friend. If the manufacturer cannot supply a full transmission data sheet the filter should be regarded as *not* suitable irrespective of what a supplier tells you.

AndyG

It is a few days too late, for what will be the damaged populous.

Still, if you still have eyes for the data sheet, after staring at the bright light.

Good luck.

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On 8/26/2017 at 15:24, Ouroboros said:

I recall viewing a partial eclipse in the 1960s through the dark bits of several photographic negatives. It doesn't bear thinking about! 

Me too in 1979's eclipse, though I viewed through glass windows to ensure more UV was being blocked.  I suppose the IR was still cooking my retina, though.  Almost 40 years on, and I see fine enough, though.

I've found I like to use an IR/UV blocking photographic filter on my eyepiece/diagonal in addition to using my Baader solar film filter.  I'd swear a significant amount of IR in particular still gets through that solar filter.  My eye feels like it's being cooked after several minutes without it.

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@Louis DWe were lucky back then and got away with it. Others may not have been so lucky.  Nevertheless, the importance of buying filters suitable for viewing the sun, from a reputable supplier, can't be emphasised strongly enough. 

I haven't noticed the effect you refer to when using Baader film. Have you found a transmission curve for the film?  I looked but couldn't find one. 

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2 hours ago, Ouroboros said:

I haven't noticed the effect you refer to when using Baader film. Have you found a transmission curve for the film?  I looked but couldn't find one.

I'll have to see if I can find the original packaging the film came in years ago to see if anything was printed on the cardboard sleeve.  However, they may have improved the product over the years.

I don't notice the cooking effect with my ST-80 and it's sub-full aperture solar filter.  I do notice it with my 8" full aperture Newt's filter.  It could just be some additive effect of larger aperture despite using film from the same sheet of material.

I'm thinking about trying Thousand Oaks's newer solar filter material.  I tried it in their solar eyeglasses for the past eclipse, and it was very sharp and didn't seem to have any cooking effect at unit power.

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I'm probably teaching grandmother to suck eggs but have you held the filter up to the light to see if their are any pinprick holes in it? I always check mine like that everytime I use it. 

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Louis,

I'm surprised to hear your "cooking effect" with the Baader solar film.

I've use it (and many other solar filters) over the years and never experienced similar.

Were you using the recommended ND5 version or the photographic ND3.8 version??

http://astrosolar.com/en/information/about-astrosolar-solar-film/astrosolar-technical-info/

 

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13 hours ago, Merlin66 said:

Louis,

I'm surprised to hear your "cooking effect" with the Baader solar film.

I've use it (and many other solar filters) over the years and never experienced similar.

Were you using the recommended ND5 version or the photographic ND3.8 version??

http://astrosolar.com/en/information/about-astrosolar-solar-film/astrosolar-technical-info/

 

I regularly check for pinprick holes, and there are none.  I store it with a protective cover in a bag.  I used whatever Baader first sold back in about the 2000-2002 timeframe for visual use.  Remember, the Texas sun is quite a bit more intense than the UK sun.  My fair skinned wife has gotten her shoulders sunburned in 20 minutes in February on a typical sunny day while hiking in open terrain and wearing a sleeveless top.  Try accomplishing that in Britain.  I think Baader needs to offer a higher ND filter for more southerly latitudes or higher elevations.  I can add a moon filter to decrease the intense brightness, but I'm not sure it blocks any IR, so I err toward the IR/UV blocking filter.  I'm considering giving the newer Thousands Oaks films a try sometime.

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Louis,

Hmmm

For the past forty years I've been observing from Australia. Summer ambient in the 40's deg C (one reason I rejected purchasing a Quark - no cooling!)

I have the transmission curve for the Baader solar film somewhere, I'll find it and upload a copy.

On the posted link, down the bottom, Baader confirm that it's safe to use with larger apertures and no IR leakage.

tov-chou-metal_coated-safe-500.jpg.6e3d1a80ea923e7a2645706d623181f3.jpg

 

 

filter_lica_baader_astrosolar_safety_film.pdf

(sorry D-ERF image also added - unable to delete!!)

 

Baader D-ERF.png

Edited by Merlin66
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