Hello ! New here with technical analogue questions...

james orme · Jun 8, 2020

Hello, thank you for accepting me !

greetings from the UK. I love taking all sorts of photos and I've never been in a dark room... Should I post a thread for my questions in a specific forum/ topic ?

I have many questions mainly to do with analogue long exposures (and modifying a Box Brownie 2a etc).
Here are a few questions to start with
How many stops are there between f/16, f/23, f/32- what would the following sequential f/ numbers in this series?

On a Box Brownie 2a what size is the smallest of the three apertures holes on the Brownie 2A : f/23 or f/32 (can't seem to find this info anywhere) ?

Photo below:
Here's a 6 hour exposure shot on a paper negative. If I went 1 stop down would I get (roughly) the same exposure result by exposing for 12 daylight hours? Likewise if I used, for example, a ND 4 filter would that mean would I get a similar result with 24 daylight hours?

Hope someone can help...

Thank you

_J

M.A.Longmore · Jun 8, 2020

.
Welcome Home James !
From The Covid Capital Of The U.S.A.

~ Ron

james orme · Jun 8, 2020

Thanks, we're not doing so badly here either...

_J

AgX · Jun 8, 2020

Welcome to Apug (now Photrio)!

Feel free to ask those qustions you never dared to ask before...

F16 > F23 = 1stop

F16 > F32 = 2stops

The ratio between any adjacent stops is 1.4.
F-figures are typically slightly rounded.

juan · Jun 8, 2020

Welcome
1. The usual stop is f/22 not 23. The next stops would be 45, 64, and 128.
2. The larger the f number, the smaller the hole, thus 32.
3. Yes, roughly.

james orme · Jun 8, 2020

Great thanks

james orme · Jun 8, 2020

Thank you AG/ Jiuan - So 1 stop down I can expose for twice as long? I'm looking for super long exposures... 4 stops down would = 4 x exposure time?

sterioma · Jun 8, 2020

james orme said:
Thank you AG/ Jiuan - So 1 stop down I can expose for twice as long?

Yes

james orme said:
. 4 stops down would = 4 x exposure time?

No. Every time you move one stop you cut time in half (or double it, depending on the direction).
So if the original time was 1/1000, then you do 1/500 (+1 stop) => 1/250 (+2 stops) => 1/125 (+3 stops) => 1/60 (+4 stops). You have gone from 1/1000 to 1/60 (which is a bigger change than 1/1000 x 4, which would be 1/250).

(Also note that for exposure times that are longer than about 1 second, you need to take into account of the "reciprocity failure", which means that you will need to progressively add more time than the simple f-stop/shutter-time relation would suggest. How much more depends on the film there are tables and calculators available online).

There are lots of resources online with detailed explanations on the correlation between f-stop, shutter time (and ISO), which I recommend getting familiar with. After a short while, these calculations will become second nature.

james orme · Jun 8, 2020

Ok thanks, I think I get it; so the photo in my post was a six hour exposure, if I put an ND4 filter on the camera it would go down 4 stops which would give me 24 hours of (daylight) exposure [6hrs x 4?]

sterioma · Jun 8, 2020

james orme said:
Ok thanks, I think I get it; so the photo in my post was a six hour exposure, if I put an ND4 filter on the camera it would go down 4 stops which would give me 24 hours of (daylight) exposure [6hrs x 4?]

When your exposure is measured in "hours" (really, already from a few seconds), then the linear relationship between f-stop and shutter times is not valid any more. You can only get an approximate "good" exposure time by looking at the specs of the particular film you are trying to use (different films have a different "reciprocity failure" curve).

(Note, though, even ignoring the "reciprocity failure", that increasing the exposure time by 4 stops is *not* the same as increasing the time 4x: it's actually (2^4)x: 1 second becomes 16, 2 seconds become 32, 3 seconds become 48, etc....)

james orme · Jun 8, 2020

Thank you very much for your insight. I think this is going to be trial and error- something that I am quite used to (especially the errors...).

ic-racer · Jun 8, 2020

You are doing pretty good so far. That 6 hour image in your first post came out great.

james orme · Jun 8, 2020

Thanks, it's a lot of fun

Black Dog · Jun 9, 2020

Hello and welcome to the forum-happy experimenting!

Hello ! New here with technical analogue questions...

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