Search results for 'back focus' - page 1226
Raynox and SR
How would a close-up add-on lens change a lens's focal length? The SR does not "see" anything through the lens, it senses camera movement and compensates. I believe the only thing it needs to know is the focal length, which it gets from the lens itself (when using a lens that communicates with t...
Posted by Jonathan-Mac on 12/04/2023 - 15:06
Raynox and SR
Adding any elements or distance between existing lens and focal plane can certainly change a lenses FL. The latter is defined as "the distance between the optical centre of a lens and the capture medium (film or sensor). That definition of a FL is only true if the image is actually in focus. The way...
Posted by Lubbyman on 12/04/2023 - 21:05
Raynox and SR
How would a close-up add-on lens change a lens's focal length? Adding any elements or distance between existing lens and focal plane can certainly change a lenses FL. The latter is defined as "the distance between the optical centre of a lens and the capture medium (film or sensor). What surpri...
Posted by petrochemist on 15/04/2023 - 11:29
Raynox and SR
I'm pretty sure that the mathematical formulae for this sort of thing was covered in A-level physics, but that was a looooong while ago :( Steve I'm sure it was, fortunately I've played with it enough to remember diopters are additive. Simply change the lenses focal length into diopters add the c...
Posted by petrochemist on 15/04/2023 - 11:42
New FA 50 1.4 lenses!!
Some pictures here: https://pentaxrumors.com/2023/05/13/first-leaked-pictures-of-the-upcoming-hd-pentax-fa-50mm-f-1-4-and-smc-pentax-fa-50mm-f-1-4-classic-lenses/ I really don't understand the logic behind producing two versions. This lens was obviously overdue a revamp and the attractive finish ...
Posted by Jonathan-Mac on 13/05/2023 - 23:27
New FA 50 1.4 lenses!!
I suspect they are already well into working on the next properly new lens, most likely a fast moderate wide (to go with the DFA* 50/1.4 and 85/1.4), these little re-vamp projects are a relatively cheap way of refreshing the line-up and will appeal to quite a few users I would imagine (cheap (relati...
Posted by pschlute on 17/05/2023 - 09:28
Macro lens for Pentax 645D
Clever people, Having got some very good feedback in I did some thinking after seeing the used price of a 645D, which would be a more long-term investment. Which of lenses specifically for the medium format would do great for macro photography of , which is going to be a project for the nex...
Posted by kasperbergholt on 14/05/2023 - 16:17
Macro lens for Pentax 645D
The technical details for Pentax 645 lenses are here: https://www.pentaxforums.com/lensreviews/SMC-Pentax-645-Medium-Format-Lenses-i4.html There are three macro lenses available - 90mm D-FA, 120mm FA and 120 A - in the section for telephoto primes. I only have experience of the 120 A, (wi...
Posted by kasperbergholt on 15/05/2023 - 17:56
K5iis and 2.8 lenses
Hello Odd question. I have read that my k5iis has a 'linear flux' central focusing point. I have been using a Pentax 16-45 as the Sigma 17-70 (HSM 2nd version without OS) seemed to miss a lot. Recently used a blower brush in the mirror box and tried using the Sigma. It now has a great hi...
Posted by Simonmac on 23/05/2023 - 09:42
Adapter advice.
Hi takuman, Here's my take on this. If you look at the K mount lens the red dot on the mount is aligned with the focus red line on the lens body. My experience is that there is an advantage with paying for a genuine Pentax adapter as then the aperture and focus points on an attached le...
Posted by MikeInDevon on 05/06/2023 - 20:40
Adapter advice.
It can be done but sooner or later you will remove the lens and the adapter will stay in the camera. It can be more trouble than you might expect. Once you get used to it you will almost certainly get more lenses from E bay - M42s are not expensive and it's fun to try them out. It's actually easier ...
Posted by Defragged on 07/06/2023 - 00:06
Repaired DFA 100 2.8 Macro
My DFA 100 2.8 Macro WR was suffering with a sticky aperture return. Prompted by a lead elsewhere on this Forum I contacted 1st Aid Repairs and got an online quote. I sent them the lens and got it back yesterday. They were very efficient and helpful - emailing me when they received the lens and ...
Posted by PeterKR on 10/06/2023 - 15:20
NEW Lens...TTartisan 100mm f/2.8 'Bubble Bokeh' M42 fit
They don't show the photo that really matters - soap bubbles with bubble bokeh :mrgreen:. I wonder what a focus stack with bubble bokeh would be like... :shock: Steve
Posted by Lubbyman on 08/08/2023 - 22:31
Dirty Lens
Hi From what I can gather from second hand lenses offered for sale by dealers, dust is by no means unusual and shouldn't detract from the image as the lens cannot actually focus on it. Hopefully, this will help Michael
Posted by MHOL190246 on 11/08/2023 - 14:56
Fungus
Spores of all sorts are extremely resistant to everything and, as has been said, they are everywhere. Experience of trying to eliminate mould from bags used to store non-photographic things in unsuitable places is that you think you've done a thorough clean but it's still hiding there and will be ba...
Posted by Lubbyman on 25/08/2023 - 10:45
Fungus
Whenever I buy an old lens that is advertised as "complete with original case" I am more wary of fungus, and the case is the first thing to go in the bin. Hear hear! The only time I've ever had a lens develop in my possession was when I cleaned a Takumar 135 and then stored it in it's leather cas...
Posted by HarisF1 on 25/08/2023 - 19:49
Pentax at 400
It's never a good thing when I start thinking about "improving" my Pentax kit, invariably it costs me money - but my view is I can usually get most of it back by re-selling some of the replaced items (or the newly acquired items if they don't do the job). My latest venture is to replace my FA*400...
Posted by LennyBloke on 01/09/2023 - 20:29
Pentax at 400
Ah! So that's the reason for the recent activity in the classifieds :wink:. Personally, I'd consider both lenses to be perfectly acceptable and decide which lens to have in the bag based on non-optical criteria (zoom or not, size, weight, handling etc.). But then I don't pixel peep and don't thin...
Posted by Lubbyman on 01/09/2023 - 23:06
Pentax at 400
Ah! So that's the reason for the recent activity in the classifieds :wink:. Personally, I'd consider both lenses to be perfectly acceptable and decide which lens to have in the bag based on non-optical criteria (zoom or not, size, weight, handling etc.). But then I don't pixel peep and don't thin...
Posted by LennyBloke on 02/09/2023 - 22:39
Tamron 17-50mm f2.8 lens with focus issue- is it something worth selling?
Hi, I have a Tamron 17-50mm f2.8 lens that has developed a slight focus issue- sometime it doesn't focus perfectly. I bought a replacement/upgraded it. So what to do with the lens; is it something that some people would be interested in buying for spares or try to repair it themselves? I've n...
Posted by dinneenp on 11/09/2023 - 16:18
