Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
06-12-2012, 02:42 PM   #16
Pentaxian
PPPPPP42's Avatar

Join Date: Jan 2012
Location: Wisconsin
Photos: Albums
Posts: 845
Original Poster
QuoteOriginally posted by RioRico Quote
2) Calculating magnification from focal length and distance: M = F/(D-F) where M is magnification, F is lens focal length, and D is subject-lens distance.
So if at 35mm my lens can focus on a piece of paper about 1397mm away (5.5") then my magnification is .026 or 1:4
.026=35mm/(1397mm-35mm)
Wheras a true macro lens is .5 (2:1) and a good one is 1 (1:1)

I guess all I needed was the math to clear things up, thats a first.

That would make my ideal macro lens this one: SMC Pentax-A 100mm F2.8 Macro Reviews - A Prime Lenses - Pentax Lens Reviews & Lens Database odd that it costs way more than the new WR FA model.

I do have to work on my technique but please don't rate the pics provided, they were 10 second planning snap shots just to give a vague idea of distance for an example. Plus I never buy training wheels, every single time I don't learn on the higher quality or pro model of something it turns out I outgrow it in a week.

Thanks all.


Last edited by PPPPPP42; 06-12-2012 at 02:53 PM.
06-12-2012, 02:57 PM   #17
Pentaxian
normhead's Avatar

Join Date: Jun 2007
Location: Near Algonquin Park
Photos: Gallery | Albums
Posts: 23,773
I thought I knew what macro was with my Sigma 70-300, after I got my Tamron 90 macro , I decided I didn't really know much of anything. AN d if you look at the work of some of the guys on here, I've pretty much decided I'll never know anything. If you're over 50 I suggest auto-focus, the old eyes just don't focus so good anymore.
06-12-2012, 03:00 PM   #18
Veteran Member
RioRico's Avatar

Join Date: Jun 2008
Location: Limbo, California
Posts: 11,264
QuoteOriginally posted by Philoslothical Quote
A given magnification (e.g. 1:1) gives the same result regardless of focal length. That's what I think he was asking. I also explained the relationship of working distance to focal length.
Yes, we can (theoretically) reach any given magnification, using any given focal length, at the right distance. I say 'theoretically' because reality intrudes upon very short lenses on our (d)SLRs. I *could* put 16mm of extension on my Zenitar 16/2.8 and *theoretically* reach 1:1. Alas, the focus distance would put the subject INSIDE the lens. Talk about bad scratches...

Working distance vs focal length breaks down this way with our (d)SLRs:

* Use a 28mm or 35mm lens either if the studio space is very small, or if we want to shoot fairly close without great magnification. A 28mm close-focus lens that reaches about 1:3.5 is great for objects down to about 13cm / 5in wide. A 35mm lens that reaches 1:1 can work (real close!) a subject about 24mm / 1in wide.

* Use a 40mm or 50mm or 60mm lens when you have or need a little more space. My MacTak 50/4(1x) also works subjects about 24mm / 1in wide, but from slightly further away. Hay, the frame is about 24mm and it's 1:1; sure, a 24mm subject fills the sensor! I consider my 40mm and 50mm macros as indoor, studio lenses.

* Use a 90mm or 100-105mm len s for even more space. Use a 150mm or 200mm for even MORE working distance. Longer than that, it gets clumsy. I don't dare put my P.Navitar 254/4.5 on 500mm extension for 1:1! Lenses of 90mm or longer are usually considered outdoor "in the field" glass. Don't scare the mantids.

Have I wandered too far afield here? Rein me in.

QuoteOriginally posted by normhead Quote
If you're over 50 I suggest auto-focus, the old eyes just don't focus so good anymore.
Ah, but AF might not focus on the point YOU want it to. Damn robots...
06-12-2012, 03:20 PM   #19
Loyal Site Supporter
pacerr's Avatar

Join Date: Jan 2008
Location: Henry, TN
Photos: Gallery | Albums
Posts: 2,852
QuoteOriginally posted by RioRico Quote
Ah, but AF might not focus on the point YOU want it to. Damn robots...
And a reminder that at some point it's much easier to attain focus by moving the camera (scrooching a l'il bit?) rather than twisting the lens. And catch-in-focus may be an option too.

06-12-2012, 05:15 PM   #20
Veteran Member




Join Date: Nov 2009
Location: Iowa
Photos: Albums
Posts: 2,269
QuoteOriginally posted by grhazelton Quote
BTW, the Promaster that GibbyTheMole mentions looks exactly like the Vivitar, which also has a Cosina incarnation.
Yep. Forgot to mention that. There's also a Phoenix version. I also forgot to mention the AF version was also sold as the Pentax SMC FA 100mm f/3.5 macro lens. The manual focus version is optically identical, but built a bit better, with smooth manual focusing, which I prefer.
06-12-2012, 06:19 PM   #21
Site Supporter
jimr-pdx's Avatar

Join Date: May 2010
Location: 1hr north of PDX
Photos: Gallery | Albums
Posts: 3,480
QuoteOriginally posted by PPPPPP42 Quote
At least one that costs less than my truck?
I see a clone of my Sigma 50/2.8 macro for under $250 - but I've never seen your truck
I really like this lens both for its macro abilities and because other than speed it's a really excellent 50mm lens. Focus limiter when you want it, aperture ring too. Oh yes, and full-frame friendly. It may not be your bowl of porridge, but I'm with Goldilocks on this lens - just right.

But if you're happy with your current setup, I'd hate to destabilize your kit. I do that often enough with mine, that's enough for me..
06-13-2012, 01:03 AM   #22
Site Supporter
rbefly's Avatar

Join Date: Oct 2009
Location: Denver, Colorado
Photos: Albums
Posts: 2,030
Short Version

Would a real macro lens improve much on what I have?
Yes.
06-13-2012, 01:45 AM   #23
Pentaxian
hoanpham's Avatar

Join Date: Nov 2009
Location: Strand
Photos: Gallery | Albums
Posts: 1,360
QuoteOriginally posted by RioRico Quote
Ah, but AF might not focus on the point YOU want it to. Damn robots...
Shot many and shot more of the same. Perhaps one should be fine?

06-13-2012, 05:34 AM   #24
Pentaxian
normhead's Avatar

Join Date: Jun 2007
Location: Near Algonquin Park
Photos: Gallery | Albums
Posts: 23,773
QuoteQuote:
Shot many and shot more of the same. Perhaps one should be fine?
That's my approach. And quite often I end up with 80% keepers and can select the best composition rather than going for one shot. I usually set the lens to it's focus point and then back out a tiny bit to be as close to 1:1 as possible.

Tamron 90 2.8 macro (capable of 1:1)



Sigma 70-300 macro ( capable of 1:2. ) While not nearly as good a lens, the Sigma can be picked up second hand for $100.

Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
distance, focus, image, inches, k-mount, lens, macro, macro lens, mode, pentax lens, range, size, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Lens for real estate photography Workingdog Pentax SLR Lens Discussion 25 03-07-2012 07:49 AM
is this lens for real ?? SMC K 18/3,5 ewig Pentax SLR Lens Discussion 18 04-19-2011 08:08 AM
HELP! The Nagging Question...Is it real or is it LENS FLARE? chefpete1 Photographic Technique 9 03-03-2011 10:01 AM
Macro Bees & Wasps - Help Improve My Macro CS13B Photo Critique 13 01-11-2011 05:32 PM
What is the best ultra wide lens for real estate photography? HermanLee Pentax SLR Lens Discussion 17 11-07-2010 11:54 AM



All times are GMT -7. The time now is 05:17 AM. | See also: NikonForums.com, part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top