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11-24-2011, 12:13 AM   #1
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I have always wanted to own a pentax but no money My son gave me a 100d with two sigma lenses a 28-90 and a 70 300 apo I just need to learn how to drive them Any advise will be greatfully recieved

11-24-2011, 01:09 AM   #2
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Welcome! If you have any specific questions, feel free to post them in the DSLR section, apart from that I would just play around with your gear

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11-25-2011, 01:43 AM   #3
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Welcome Telegazz. I've got back into hobby photography after a 20yr gap. Loving my new Pentax so far. You'll find lots of good advice on the forums.
11-25-2011, 03:22 AM   #4
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QuoteOriginally posted by telegazz Quote
I have always wanted to own a pentax but no money My son gave me a 100d with two sigma lenses a 28-90 and a 70 300 apo I just need to learn how to drive them Any advise will be gratefully received
Welcome, mate. Once you start to use this kit, I think you'll find the 28mm min. FL a bit limiting. Like when you're trying to shoot a group of 3 or 4 people in a normal room in a house. That's when you'll appreciate the usefulness of a 16-18mm FL.

I bought a lens with a similar FL range, the Pentax-F 35-105/f4-5.6, but I've rarely used it because I found both the 35mm min. FL and small aperture not very useful indoors.

The 70-300mm FL should be OK for good daylight, but for action where you need a fast shutter speed, or in low light, these situations will bring up limitations due to the large f-number at the 300mm end of the zoom range (aperture get smaller as the f-number get bigger, so the aperture opening of f/4 is bigger than f/5.6, just as the fraction 1/4 is bigger than either 1/5.6 or 1/8). Also this lens needs to have the aperture closed to f/8-f/9.5 to get the sharpest overall result, meaning even less light reaching the sensor.

What you've got will be useful to learn the basics. I started out with a K100D Super + Sigma 18-50/f3.5-5.6 . This lens is usually panned as a poor lens, but it was cheap. The cheapest way to get a substantial improvement in quality will be to buy an old 50mm M or A series Pentax f/1.4 or f/1.7 "prime" (non-zoom) lens. Best bang for the buck in old prime lenses is possibly the Pentax-M 50/f1.7.

I think the Sigma 28-90 is a f/3.5-f/5.6 design. That probably means that at 50mm FL, its aperture is about f/4-4.5. The difference in stops, wide open, at 50mm between this and the M lens I've mentioned is: f/1.7 -> f/2 (0.45 stops) -> f/2.8 (1.45 stops) -> f/4 (2.45 stops) -> f/4.5 (2.75 stops). Let's call it a 2.5 stops difference. That means if we are operating both lens on the K100D, with fully open apertures, and the same shutter speed, say 1/100s, then if we can operate the K100D at min. ISO sensitivity (ISO 200) with the f/1.7 lens then, when using the Sigma, because of the 2.5 stops smaller aperture, you would need to bump the ISO up correspondingly to get the same exposure i.e. ISO200 -> ISO400 (1 stop) -> ISO800 (2 stops) - > ISO1100 (2.5 stops). Now I never like using the K100D Super above ISO800 because of the visible noise, so the "faster" f/1.7 lens will give you less noisy shots in many situations.

Small f-numbers/large apertures will also allow you to use a shallow Depth-of-Field to get subject from background isolation due to the strong out-of-focus blurring of a distracting background. This shallow DOF is a popular feature of large aperture lenses. It can also make it difficult to get all of a close-up object, say a flower or a face, all in focus.

And the M50/f1.7 has a good reputation for sharpness. What it doesn't have is auto-focus (AF) or auto-exposure (AE). So getting this M lens (I bought a M50/f2, then M50/f1.7, then A50/f2, then sold the M50/f2, all on ebay) will encourage you to learn about exposure rather than relying on the camera to do everything. It means it takes longer to take a shot, so you can concentrate more on each shot (a "deliberative" approach), rather than pray-and-spraying away with an auto lens.

I'd recommend Digital Camera Tips and Reviews: Photonhead, The Essence of Modern Film and Digital Photography as a good site to learn the basics, particularly the SimCam camera simulator.


Last edited by dosdan; 11-25-2011 at 03:50 AM.
11-25-2011, 03:47 AM   #5
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Good to have you here mate.
Start with just experimenting with your shooting style and technique, then move ahead with some background reading on the basics of photography.
Then we expect to find you back here with more questions.
Enjoy the journey.
11-25-2011, 05:49 AM   #6
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Thanks for all the info it looks like I have a lot to learn but at least I have plenty of time to do it

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